JP2012225266A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine which is applied to an internal combustion engine having a catalyst to perform air-fuel ratio control and exhaust gas temperature control.SOLUTION: This control device includes: an air-fuel ratio control means for changing the quantity of fuel to be supplied to the engine according to a first change quantity determined so that the air-fuel ratio of an air-fuel mixture coincides with the target air-fuel ratio; and an exhaust gas temperature control means for changing the quantity of fuel to be supplied to the internal combustion engine according to a second change quantity determined so as to lower the temperature of exhaust gas. The control device determines the first change quantity and a second change quantity in a fourth point of time so that the sum of the first change quantity and the second change quantity in the fourth point of point of time in a catalyst temperature control period is equal to or larger than the first change quantity in a first point of time, when the air-fuel ratio is controlled in the first point of time and at least the exhaust gas temperature control out of the air-fuel ratio control and the exhaust gas temperature control is performed in the catalyst temperature control period which is a period up to a third point of time after a second point of time, from the first point of time or the second point of time after the first point of time.

Description

  The present invention relates to a control device applied to an internal combustion engine equipped with a catalyst.

  Gas (exhaust gas) discharged from the combustion chamber of the internal combustion engine contains various substances. Therefore, conventionally, an internal combustion engine provided with a catalyst for purifying exhaust gas by removing these substances from the exhaust gas has been proposed. Examples of such a catalyst include a so-called three-way catalyst and a NOx storage reduction catalyst. As is well known, these catalysts have a catalyst temperature equal to or higher than a specific activation temperature, and the exhaust gas has an oxygen concentration (a mixture obtained by mixing air and fuel at a stoichiometric air-fuel ratio). When the oxygen concentration is in the vicinity of the oxygen concentration of the exhaust gas generated when the gas is burned (hereinafter also referred to as “reference oxygen concentration” for convenience), the exhaust gas can be purified at a high purification rate. Hereinafter, for convenience, the three-way catalyst, the NOx storage reduction catalyst, and the like are simply referred to as “catalyst”.

  As described above, in order for the exhaust gas to be purified at a high purification rate, the temperature of the catalyst needs to be equal to or higher than the activation temperature. The temperature of the catalyst increases, for example, when the catalyst is heated to the exhaust gas. However, if the temperature of the catalyst becomes excessively high, the exhaust gas purification performance of the catalyst may deteriorate due to thermal denaturation of the substances constituting the catalyst (for example, noble metals, oxygen storage substances, and carriers). is there. Thus, one of the conventional control devices for internal combustion engines (hereinafter also referred to as “conventional device”) pays attention to the correlation between the temperature of the catalyst and the temperature of the exhaust gas, and is included in the air-fuel mixture. The temperature of the catalyst is controlled by adjusting the amount of fuel (in other words, the amount of fuel supplied to the internal combustion engine).

  More specifically, the conventional device estimates the temperature of the catalyst based on the operating state of the internal combustion engine. In the conventional apparatus, when the estimated temperature of the catalyst is equal to or higher than a predetermined upper limit temperature, the amount of fuel supplied to the internal combustion engine is compared with the amount of the fuel when the temperature of the catalyst is not higher than the upper limit temperature. Increase. This increases the amount of energy consumed when the fuel is vaporized, thus reducing the amount of energy discharged into the exhaust gas. As a result, the temperature of the exhaust gas is lowered from the same temperature when the amount of fuel is not increased, so that the temperature of the catalyst can be prevented from becoming excessively high (see, for example, Patent Document 1). Hereinafter, the fact that the temperature of exhaust gas is lowered by increasing the amount of fuel is also referred to as “fuel cooling effect”.

JP 2006-37921 A

  As described above, in an internal combustion engine equipped with a catalyst, the temperature of exhaust gas is lowered by increasing the amount of fuel supplied to the engine. And it can prevent that the temperature of a catalyst becomes high too much by reducing the temperature of waste gas. Hereinafter, for convenience, control for reducing the temperature of exhaust gas by adjusting the amount of fuel is also referred to as “exhaust gas temperature control”.

  Incidentally, as described above, in order to purify the exhaust gas at a high purification rate, it is required that the oxygen concentration of the exhaust gas is a specific oxygen concentration (oxygen concentration in the vicinity of the reference oxygen concentration). The oxygen concentration of the exhaust gas changes in relation to the air-fuel ratio of the air-fuel mixture, for example. Therefore, in an internal combustion engine equipped with a catalyst, for example, the amount of fuel contained in the air-fuel mixture is adjusted so that the oxygen concentration of the exhaust gas matches the oxygen concentration in the vicinity of the reference oxygen concentration. And the state by which exhaust gas is purified with a high purification rate can be maintained by controlling the oxygen concentration of exhaust gas. Hereinafter, for convenience, controlling the air-fuel ratio of the air-fuel mixture by adjusting the amount of fuel is also referred to as “air-fuel ratio control”.

  Thus, in an internal combustion engine equipped with a catalyst, the amount of fuel can be changed by both exhaust gas temperature control and air-fuel ratio control. Conversely, the amount of fuel can affect both exhaust gas temperature control and air-fuel ratio control. Therefore, if the correlation between the exhaust gas temperature control and the air-fuel ratio control is not sufficiently considered and each of these controls is performed independently, the purpose of one or both of these controls may not be sufficiently achieved. it is conceivable that.

  In view of the above problems, an object of the present invention is to provide a control device for an internal combustion engine that can achieve the purposes of exhaust gas temperature control and air-fuel ratio control as appropriately as possible.

  A control device according to the present invention for solving the above problems is applied to an internal combustion engine including a catalyst for purifying gas (exhaust gas) discharged from a combustion chamber of the internal combustion engine.

  The catalyst is not particularly limited as long as it can purify exhaust gas. As the catalyst, for example, a known three-way catalyst having a noble metal as a catalyst component and a carrier containing an oxygen storage material can be employed. Furthermore, as the catalyst, for example, a known NOx storage reduction catalyst having a noble metal as a catalyst component and a carrier containing an oxygen storage material and a NOx storage material can be employed.

  The above-mentioned “purifying exhaust gas” means removing at least a part of the purification target substances such as nitrogen oxides and unburned substances contained in the exhaust gas from the exhaust gas, and not all of the purification target substances are required. It does not mean to be removed from the exhaust gas.

  A control device of the present invention applied to an internal combustion engine provided with the catalyst includes air-fuel ratio control means and exhaust gas temperature control means.

  The air-fuel ratio control means is means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine. The air-fuel ratio control means changes the amount of fuel supplied to the internal combustion engine in accordance with “a first change amount determined so that the air-fuel ratio matches the target air-fuel ratio”.

  As is well known, the air-fuel mixture is a gas containing air and fuel. As is well known, the air-fuel ratio is a ratio (A / F) of the amount (A) of air contained in the mixture to the amount (F) of fuel contained in the mixture. Therefore, if the amount of air is constant (fixed value), the air-fuel ratio decreases when the amount of fuel increases, and the air-fuel ratio increases when the amount of fuel decreases.

  The target air-fuel ratio is not particularly limited as long as it is set to an appropriate value in consideration of the exhaust gas purification rate by the catalyst. For example, as the target air-fuel ratio, a stoichiometric air-fuel ratio or a value slightly smaller than the stoichiometric air-fuel ratio can be adopted. As is well known, the stoichiometric air-fuel ratio represents an air-fuel ratio (in terms of mass ratio, about 14.7) at which air and fuel react without excess or deficiency when the air-fuel mixture burns.

  Hereinafter, an air-fuel ratio smaller than the stoichiometric air-fuel ratio is also referred to as “rich air-fuel ratio”, and an air-fuel ratio greater than the stoichiometric air-fuel ratio is also referred to as “lean-side air-fuel ratio”. That is, the amount of fuel included in the unit amount of the air-fuel mixture that is the “rich air-fuel ratio” is larger than the amount of fuel included in the unit amount of the air-fuel mixture that is the stoichiometric air-fuel ratio. Conversely, the amount of fuel contained in the unit amount of the air-fuel mixture that is the “lean air-fuel ratio” is smaller than the amount of fuel contained in the unit amount of the air-fuel mixture that is the stoichiometric air-fuel ratio.

  The first change amount is not particularly limited as long as it is a “fuel amount change amount” determined so that the air-fuel ratio matches the target air-fuel ratio. A positive value, a negative value, or zero is adopted as the first change amount. For example, when the first change amount is determined according to the concept of feedback control, a feedback amount determined based on the difference between the actual oxygen concentration of the exhaust gas and the reference oxygen concentration can be adopted as the first change amount.

  The exhaust gas temperature control means is means for controlling the temperature of the exhaust gas. The exhaust gas temperature control means changes the amount of fuel supplied to the internal combustion engine in accordance with “a second change amount determined so as to lower the temperature of the exhaust gas”.

  The second change amount is not particularly limited as long as it is a “change amount of the fuel amount” determined so as to lower the temperature of the exhaust gas. As described above, when the amount of fuel is increased, the temperature of the exhaust gas can be lowered due to the fuel cooling effect. Therefore, either a positive value or zero is adopted as the second change amount. For example, as the second change amount, a change amount determined based on the operating state of the internal combustion engine when the temperature of the catalyst may become excessively high may be employed.

  As described above, in the control device of the present invention, “both” of the air-fuel ratio control means and the exhaust gas temperature control means change the amount of fuel supplied to the internal combustion engine. For this reason, when the first change amount and the second change amount are determined without considering the correlation between these control means, either or both of the control of the air-fuel ratio of the air-fuel mixture and the control of the temperature of the exhaust gas are not appropriately performed. There seems to be a possibility.

  Therefore, in the control device of the present invention, the first change amount and the second change amount are determined in consideration of the correlation between the air-fuel ratio control means and the exhaust gas temperature control means.

Specifically,
(A-1) The air-fuel ratio is controlled at the “first time point”, and
(A-2) The empty period during the “catalyst temperature control period, which is a period from the first time point or the second time point after the first time point to the third time point after the second time point”. When at least the control of the temperature of the exhaust gas among the control of the fuel ratio and the control of the temperature of the exhaust gas is performed,
(B) “A total of the first change amount and the second change amount at the“ fourth time point during the catalyst temperature control period ”is equal to or greater than the first change amount at the“ first time point ”. The first change amount and the second change amount at the “fourth time point” are determined.

  Hereinafter, the reason why the first change amount and the second change amount are determined as described above in the control device of the present invention will be described. As can be understood from the above (A-1), (A-2), and (B), the first time point to the fourth time point are the first time point, the second time point, and the fourth time point in time series. And in the order of the third time point.

  First, when the air-fuel ratio is being controlled ((A-1) above), the amount of fuel is adjusted so that the air-fuel ratio of the air-fuel mixture matches the target air-fuel ratio (that is, according to the first change amount). The Next, when control of the temperature of the exhaust gas is started at a certain time point (first time point or second time point) (above (A-2)), the temperature of the exhaust gas is decreased (that is, according to the second change amount). ) The amount of fuel begins to be adjusted. During the period in which the exhaust gas temperature is controlled, the air-fuel ratio control may be “stopped” or “continued”. The period during which “at least the exhaust gas temperature control” of the air-fuel ratio control and exhaust gas temperature control is performed is also referred to as a catalyst temperature control period (above (A-2)).

  For example, when the control of the air-fuel ratio is “stopped” in the period during which the exhaust gas temperature is controlled (catalyst temperature control period), the “first change amount” at a certain point in time (fourth point) is “ Zero. Here, the “second change amount” at that time point (fourth time point) is the time point before the time point when the control of the exhaust gas temperature is started or the time point when the same control is started (that is, the same control is started). Previous time point, in other words, the amount of fuel before the start of exhaust gas temperature control when it is “smaller” than the fuel amount change amount (first change amount by air-fuel ratio control) at the first time point) Rather, the amount of fuel after the control is started is “small”. In other words, in this case, when control of the temperature of the exhaust gas is started, the amount of fuel is “decreased”. As a result, in this case, the fuel cooling effect cannot be obtained properly, and the temperature of the exhaust gas may not be lowered appropriately.

  On the other hand, for example, when the control of the air-fuel ratio is “continued” in the catalyst temperature control period, the “first change amount” at the fourth time point is “positive value, negative value or zero”. Here, when the “total of the first change amount and the second change amount” at the fourth time point is “smaller” than the first change amount at the first time point, as before, before the control of the exhaust gas temperature is started. Therefore, the amount of fuel after the start of the control is “smaller” than the amount of fuel. As a result, even in this case, the temperature of the exhaust gas may not be appropriately reduced.

  As described above, there is a possibility that the temperature control of the exhaust gas is not appropriately performed even when the control of the air-fuel ratio is stopped or continued during the catalyst temperature control period. Therefore, in the control device of the present invention, "the sum of the first change amount and the second change amount at the fourth time point during the catalyst temperature control period is equal to or greater than the first change amount at the first time point" A first change amount and a second change amount at the fourth time point are determined.

  Accordingly, the sum of the first change amount and the second change amount at an arbitrary time point (fourth time point) in the catalyst temperature control period is always the first change amount “before the catalyst temperature control period (first time point)”. That's it. In other words, the amount of fuel during the catalyst temperature control period is always “larger” than the amount of fuel before the catalyst temperature control period. Therefore, since the fuel cooling effect is appropriately obtained in the catalyst temperature control period, the temperature of the exhaust gas is appropriately reduced during the same period. Therefore, the temperature of the catalyst is prevented from becoming excessively high. As a result, the control device of the present invention has a purpose of controlling the temperature of the exhaust gas and the control of the air-fuel ratio compared to the case where the control by the control device of the present invention is not performed (in particular, the purpose of controlling the temperature of the exhaust gas). Can be achieved appropriately.

  Hereinafter, some aspects of the control device of the present invention will be described.

In one aspect of the control device of the present invention,
As the catalyst temperature control period, one of “the current temperature of the catalyst that is the temperature of the catalyst at the current time point” and “the convergence temperature of the catalyst that is the temperature that the temperature of the catalyst is estimated to reach at a future time point” A period in which at least one is determined to be equal to or higher than the threshold temperature during the catalyst temperature control period may be employed.

  The current temperature of the catalyst may be an actual temperature at the current time point or an estimated temperature at the current time point. For example, the temperature acquired by a temperature sensor etc. may be adopted as the actual temperature of the catalyst. On the other hand, for example, as the estimated temperature of the catalyst, the temperature estimated based on the operating state of the internal combustion engine, the temperature estimated based on the exhaust gas temperature, and the temperature estimated based on the convergence temperature of the catalyst, Etc. may be employed.

  The convergence temperature of the catalyst may be higher or lower than the current temperature of the catalyst. Of course, the convergence temperature may coincide with the current temperature. As the convergence temperature of the catalyst, for example, a temperature estimated based on the operating state of the internal combustion engine, a temperature estimated based on the temperature of the exhaust gas, and the like can be employed.

  The threshold temperature is not particularly limited as long as it is an appropriate value determined in consideration of the heat resistance of the catalyst. For example, as the threshold temperature, a temperature at which at least one of the current temperature of the catalyst and the convergence temperature of the catalyst is equal to or higher than the threshold temperature, a temperature at which the exhaust gas purification performance of the catalyst may be determined to deteriorate may be adopted. Can be done.

  As described above, the exhaust gas temperature is controlled in the catalyst temperature control period. The control of the temperature of the exhaust gas is desirably performed when it is determined that the temperature of the catalyst may become excessively high. Therefore, in this embodiment, as the catalyst temperature control period, a period in which “at least one of the current catalyst temperature and the convergence temperature of the catalyst” is determined during the same period as being equal to or higher than a predetermined threshold temperature. Is adopted. Thereby, the control apparatus of this invention can prevent more reliably that the temperature of a catalyst becomes high too much.

Furthermore, in another aspect of the control device of the present invention,
As the first change amount, a change amount based on a “basic amount” that is an amount of fuel determined based on the target air-fuel ratio may be employed. Further, as the second change amount, a change amount based on the basic amount can be adopted.

  As the basic amount, for example, the amount of air introduced into the internal combustion engine that can be determined based on the operating state of the internal combustion engine, the amount of fuel calculated based on the target air-fuel ratio, and the like can be adopted. .

  By the way, in the control device of the present invention, “the sum of the first change amount and the second change amount at an arbitrary time point (fourth time point) during the catalyst temperature control period is always before the catalyst temperature control period (first time). The first change amount and the second change amount are determined so as to be equal to or greater than the first change amount at the time). Hereinafter, some examples of a method for determining the first change amount and the second change amount will be described before the description of the aspect of the control device of the present invention is continued.

First, as a first example,
When the second change amount determined at the fourth time point is “smaller” than the first change amount at the first time point, the control of the air-fuel ratio and the exhaust gas temperature control at the fourth time point “ Both "can be done.

  In this example, in the above case, “both” of the control of the air-fuel ratio and the temperature of the exhaust gas are performed at the fourth time point (any time point during the catalyst temperature control period). In other words, the control of the air-fuel ratio is “continued” during the catalyst temperature control period. As a result, the change amount at the fourth time point is the sum of the change amount (first change amount) for the control of the air-fuel ratio and the change amount (second change amount) for the control of the exhaust gas temperature. Here, it can be considered that the first change amount at the fourth time point is substantially the same as the first change amount at the first time point unless the basic amount fluctuates. Therefore, at least when the basic amount does not change, the sum of the first change amount and the second change amount is equal to or greater than the first change amount at the first time point. Thereby, it can prevent appropriately that the temperature of a catalyst becomes high too much.

By the way, in the first example described above,
As the target air-fuel ratio at the fourth time point, “an air-fuel ratio smaller than the target air-fuel ratio at the first time point” may be employed.

  When the amount of fuel is “increased” by controlling the temperature of the exhaust gas (in order to obtain a fuel cooling effect), the air-fuel ratio of the air-fuel mixture moves away from the target air-fuel ratio toward the rich air-fuel ratio (in other words, , So that the air-fuel ratio decreases). On the other hand, as described above, the air-fuel ratio control means changes the amount of fuel so that the air-fuel ratio of the air-fuel mixture matches the target air-fuel ratio. Therefore, when the amount of fuel is “increased” as described above, if the air-fuel ratio is controlled, the amount of fuel may be “decreased” so that the air-fuel ratio of the mixture approaches the target air-fuel ratio. It is believed that there is. In other words, the amount of change (increase) resulting from the control of the exhaust gas temperature is scraped by the amount of change (decrease) resulting from the control of the air-fuel ratio (hereinafter also referred to as “eroded”). .) As a result, it is considered that the amount of fuel may not be increased to the extent that the temperature of the exhaust gas is appropriately reduced.

  Therefore, in the first example, “a value smaller than the target air-fuel ratio before the start of control of exhaust gas temperature (first time)” can be adopted as the target air-fuel ratio at the fourth time point. As a result, the temperature of the exhaust gas can be more appropriately lowered than when the target air-fuel ratio at the fourth time point is the same as the target air-fuel ratio at the first time point.

Furthermore, in the first example described above,
As the target air-fuel ratio at the fourth time point, “the value (C) obtained by dividing the sum of the second change amount and the basic amount at the fourth time point by the basic amount, The air / fuel ratio (AF / C) obtained by dividing the target air / fuel ratio (AF) ”may be employed.

  The above “value (C) obtained by dividing the sum of the second change amount and the basic amount at the fourth time point by the basic amount” is “a value obtained by converting the second change amount into a change rate with respect to the basic amount”. It can be paraphrased. For example, when the second change amount corresponds to a predetermined proportion of the basic amount (for example, 5% of the basic amount), the “value obtained by dividing (C)” is a value (for example, 1.05). Therefore, the air / fuel ratio (AF / C) obtained by dividing the target air / fuel ratio (AF) at the first time point by the value (C) is smaller than the target air / fuel ratio (AF) at the first time point (AF). /1.05). Thus, the target air-fuel ratio (AF / C) at the fourth time point is smaller as the second change amount is larger.

  More specifically, if the amount of air (GA) contained in the air-fuel mixture is the same at the first time point and the fourth time point, it corresponds to the target air-fuel ratio (AF / 1.05) obtained by the above division. The basic amount (1.05 × GA / AF) to be obtained is obtained by multiplying the basic amount (GA / AF) corresponding to the original target air-fuel ratio (AF) by the above “value corresponding to the ratio (1.05)”. Equal to the value. Therefore, according to this example, when the second change amount corresponds to a predetermined proportion (5%) of the basic amount, the basic amount is changed by that proportion (5%) (multiplied by 1.05).

  As a result, when the amount of fuel is increased by the second change amount (to increase the fuel amount by 5%) by controlling the temperature of the exhaust gas (to increase the fuel cooling effect), the basic amount is also increased according to the second change amount. (It will be multiplied by 1.05). Therefore, even if the air-fuel ratio control is performed in parallel with the exhaust gas temperature control, the “change amount (increase) caused by the second change amount” is not eroded by the air-fuel ratio control. The amount of fuel is reliably increased by the second change amount. Thereby, the temperature of exhaust gas can be reduced more appropriately.

  The symbols “C” and “AF”, and the numerical values “5%” and “1.05” are merely used with the intention that the present invention can be easily understood by them, They are not intended to be construed as limiting the content of the invention.

Then, as a second example:
When the second change amount determined at the fourth time point is smaller than the first change amount at the first time point, the second change amount is “corrected” to an amount greater than or equal to the first change amount. In the fourth time point, only “control of the temperature of the exhaust gas” of the control of the air-fuel ratio and the control of the temperature of the exhaust gas can be performed.

  In this example, at the fourth time point (arbitrary time point during the catalyst temperature control period), only “control of the exhaust gas temperature” of the air-fuel ratio control and the exhaust gas temperature control is performed. In other words, the control of the air-fuel ratio is “stopped” during the catalyst temperature control period. However, in this example, the second change amount at the fourth time point is corrected to “a value greater than or equal to the first change amount at the first time point”. As a result, the sum of the first change amount and the second change amount at the fourth time point (in practice, only the second change amount) is always greater than or equal to the first change amount at the first time point. Further, since the air-fuel ratio control is not performed at the fourth time point, the second change amount is not eroded by the air-fuel ratio control. Thereby, the temperature of exhaust gas can be reduced more appropriately.

Then, as a third example:
When the second change amount determined at the fourth time point is smaller than the first change amount at the first time point, the second change amount is “the sum of the second change amount and the first change amount”. Then, at the fourth time point, “only the control of the exhaust gas temperature” among the control of the air-fuel ratio and the control of the temperature of the exhaust gas can be performed.

  Also in this example, at the fourth time point, only “control of exhaust gas temperature” out of control of air-fuel ratio and exhaust gas temperature is performed. However, in this example, the second change amount at the fourth time point is corrected to “the sum of the first change amount at the first time point and the second change amount”. As a result, the sum of the first change amount and the second change amount at the fourth time point (in practice, only the second change amount) is equal to or greater than the first change amount at the first time point. Further, as described above, since the air-fuel ratio control is not performed at the fourth time point, the second change amount is not eroded by the air-fuel ratio control. Thereby, the temperature of exhaust gas can be reduced more appropriately.

Furthermore, in the fourth example:
As the second change amount, “the reference change amount determined based on the operating state of the internal combustion engine and larger than the first change amount at the first time point” is set to “the current temperature of the catalyst is the convergence temperature of the catalyst. The “correction change amount” obtained by multiplying the “correction coefficient that approaches 1” as it approaches can be adopted.

  As described above, the second change amount may be a change amount of the amount of fuel determined so as to decrease the temperature of the exhaust gas. In this example, a “reference change amount” is determined based on the operating state of the internal combustion engine, and this reference change amount is corrected in consideration of the temperature of the catalyst. Thereby, the second change amount at the fourth time point can be determined as an appropriate amount corresponding not only to the operating state of the internal combustion engine but also to the temperature of the catalyst.

The method for determining the correction coefficient is not particularly limited. For example, in the fourth example,
As the correction coefficient, “the difference between the current temperature (P) of the catalyst and the threshold temperature (T)” is divided by the “difference between the convergence temperature (F) of the catalyst and the threshold temperature (T)”. The resulting value ((PT) / (FT)) can be employed.

  The above are several examples of the method for determining the first change amount and the second change amount in the control device of the present invention.

Returning to the description of the aspect of the control apparatus of the present invention, in still another aspect of the control apparatus of the present invention,
As the target air-fuel ratio at the first time point, a “theoretical air-fuel ratio” can be adopted.

  As described above, the catalyst can purify the exhaust gas at a high purification rate when the oxygen concentration of the exhaust gas is in the vicinity of the reference oxygen concentration. Therefore, in this aspect, the stoichiometric air-fuel ratio is employed as the target air-fuel ratio at the first time point (that is, the time point before the start of the exhaust gas temperature control, the time point when the air-fuel ratio control is performed). . Thereby, the control apparatus of the present invention can purify the exhaust gas at a high purification rate at the first time point.

By the way, in the control apparatus of the present invention including the several aspects described above,
As the catalyst, when the oxygen concentration of the exhaust gas deviates “in the direction in which the oxygen concentration increases” from the reference oxygen concentration that is the oxygen concentration of the exhaust gas generated when the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio, The purification rate of “nitrogen oxides” contained in the exhaust gas by the catalyst decreases at the first reduction rate, and the oxygen concentration of the exhaust gas deviates from the reference oxygen concentration “in a direction in which the oxygen concentration decreases”. In this case, a catalyst having a characteristic that the purification rate of the nitrogen oxides is reduced at a second reduction rate smaller than the first reduction rate may be employed.

  As described above, the catalyst purifies the exhaust gas by removing various substances contained in the exhaust gas from the exhaust gas. The purification rate of these substances by exhaust gas is generally considered to be different in relation to the type of these substances and also in relation to the oxygen concentration of the exhaust gas.

  Therefore, from the viewpoint of efficiently purifying nitrogen oxide (NOx) contained in the exhaust gas, a catalyst having the above characteristics can be employed as a catalyst provided in the control device of the present invention. This catalyst indicates that the reduction rate of the purification rate (second reduction rate) when the oxygen concentration of the exhaust gas moves away from the reference oxygen concentration in the direction in which the oxygen concentration becomes smaller. It is smaller than the same decrease rate (first decrease rate) when moving away in the direction of increasing density.

  Note that the direction in which the oxygen concentration of exhaust gas decreases corresponds to the direction in which the air-fuel ratio decreases (rich side). Also, the direction in which the oxygen concentration of the exhaust gas increases corresponds to the direction in which the air-fuel ratio increases (lean side).

  As described above, in the control device of the present invention, the amount of fuel during the catalyst temperature control period is greater than the amount of fuel before the catalyst temperature control period (that is, the oxygen concentration of the exhaust gas is reduced, and the air-fuel ratio is reduced. The first change amount and the second change amount are determined so as to be on the rich side. Therefore, for example, when the target air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio “before” the catalyst temperature control period (in this case, the oxygen concentration of the exhaust gas is considered to be the reference oxygen concentration), the catalyst. The oxygen concentration of the exhaust gas during the temperature control period “medium” is considered to be an oxygen concentration smaller than the reference oxygen concentration. Even if the target air-fuel ratio of the air-fuel mixture before the catalyst temperature control period is not set to the stoichiometric air-fuel ratio, the oxygen concentration of the exhaust gas during the catalyst temperature control period is less than the reference oxygen concentration. There may be cases.

  If the catalyst has the above characteristics, even if the oxygen concentration of the exhaust gas during the catalyst temperature control period is smaller (richer side) than the reference oxygen concentration, the oxygen concentration is larger than the reference oxygen concentration (lean). The nitrogen oxide can be purified at a higher purification rate than in the case of the oxygen concentration on the side). As a result, the control device of the present invention can appropriately reduce the temperature of the exhaust gas while suppressing as much as possible the reduction in the purification rate of nitrogen oxides by the catalyst. That is, the control device of the present invention can achieve the purposes of exhaust gas temperature control and air-fuel ratio control as appropriately as possible.

  The nitrogen oxide purification rate is not particularly limited as long as it is a value representing the degree of nitrogen oxide purification. For example, the purification rate of nitrogen oxides includes the ratio of the amount of nitrogen oxides contained in the unit amount of exhaust gas discharged from the catalyst to the amount of nitrogen oxides contained in the unit amount of exhaust gas introduced into the catalyst, etc. Can be employed. Moreover, the reduction rate of the said purification rate should just be a value showing the grade of the reduction of a purification rate, and is not restrict | limited in particular. For example, as the reduction rate of the purification rate, when the oxygen concentration of the exhaust gas deviates from the reference oxygen concentration, the reduction amount of the purification rate per unit oxygen concentration can be adopted.

1 is a schematic view of an internal combustion engine to which a control device according to a first embodiment of the present invention is applied. It is a graph which shows the relationship between the purification rate of the exhaust gas by a catalyst, and an air fuel ratio. 2 is a graph showing a relationship between an output value of an upstream air-fuel ratio sensor shown in FIG. 1 and an air-fuel ratio. 2 is a graph showing a relationship between an output value of a downstream air-fuel ratio sensor shown in FIG. 1 and an air-fuel ratio. It is a schematic flowchart which shows the action | operation of the control apparatus which concerns on the 1st Embodiment of this invention. It is a time chart which shows an example of control by a reference example. It is a time chart which shows an example of control by a 1st embodiment. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 1st Embodiment of this invention performs. It is a time chart which shows an example of control by a 2nd embodiment. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 2nd Embodiment of this invention performs. It is a time chart which shows an example of control by a 3rd embodiment. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 3rd Embodiment of this invention performs. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 3rd Embodiment of this invention performs. It is a time chart which shows an example of control by a 4th embodiment. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 4th Embodiment of this invention performs. It is a time chart which shows an example of control by a 5th embodiment. It is the flowchart which showed the routine which CPU of the control apparatus which concerns on 5th Embodiment of this invention performs.

  Embodiments (first embodiment to fifth embodiment) of an internal combustion engine control apparatus according to the present invention will be described below with reference to the drawings.

(First embodiment)
<Outline of device>
FIG. 1 shows a schematic configuration of a system in which a control device (hereinafter also referred to as “first device”) according to a first embodiment of the present invention is applied to an internal combustion engine 10. The internal combustion engine 10 is a four-cycle spark ignition multi-cylinder (four-cylinder) engine. FIG. 1 shows only a cross section of one of a plurality of cylinders. The other cylinders also have the same configuration as this one cylinder. Hereinafter, “internal combustion engine 10” is also simply referred to as “engine 10”.

  The engine 10 includes a cylinder block portion 20, a cylinder head portion 30 fixed to the upper portion of the cylinder block portion 20, and an intake system for introducing a gas (air mixture) in which air and fuel are mixed into the cylinder block portion 20. 40, an exhaust system 50 for releasing gas (exhaust gas) discharged from the cylinder block unit 20 to the outside of the engine 10, an accelerator pedal 61, various sensors 71 to 78, and an electronic control unit 80 are provided. .

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The piston 22 reciprocates in the cylinder 21, and the reciprocating motion of the piston 22 is transmitted to the crankshaft 24 via the connecting rod 23, whereby the crankshaft 24 is rotated. The inner wall surface of the cylinder 21, the upper surface of the piston 22, and the lower surface of the cylinder head portion 30 define a combustion chamber 25.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake cam shaft that drives the intake valve 32, and a phase angle and lift amount of the intake cam shaft are continuously provided. Variable intake timing device 33 to be changed, actuator 33a of variable intake timing device 33, injector 34 for injecting fuel into intake port 31, exhaust port 35 communicating with combustion chamber 25, and exhaust valve 36 for opening and closing exhaust port 35 And an exhaust camshaft 37 for driving the exhaust valve 36, an ignition plug 38, and an igniter 39 including an ignition coil for generating a high voltage to be applied to the ignition plug 38.

  The intake system 40 includes an intake manifold 41 that communicates with each cylinder via an intake port 31, an intake pipe 42 that is connected to a collective portion on the upstream side of the intake manifold 41, and an air cleaner that is provided at the end of the intake pipe 42. 43, a throttle valve (intake throttle valve) 44 that can change the opening area (opening cross-sectional area) of the intake pipe 42, and a throttle valve actuator 44a that rotates the throttle valve 44 in response to an instruction signal. ing. The intake port 31, the intake manifold 41, and the intake pipe 42 constitute an intake passage.

  The exhaust system 50 includes an exhaust manifold 51 connected to each cylinder via an exhaust port 35, an exhaust pipe 52 connected to a downstream portion of the exhaust manifold 51, and exhaust gas purification provided in the exhaust pipe 52. Catalyst 53. The exhaust port 35, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage. Hereinafter, the exhaust gas-purifying catalyst 53 is also simply referred to as “catalyst 53”.

  The catalyst 53 is a three-way catalyst including a ceria / zirconia cocatalyst (CeO2-ZrO2) as an oxygen storage material, ceramics such as alumina as a support, and noble metals such as platinum and rhodium as catalyst components. The catalyst 53 is generated when the temperature of the catalyst is equal to or higher than a predetermined activation temperature, and the oxygen concentration of the exhaust gas introduced into the catalyst 53 is the reference oxygen concentration (as described above, the stoichiometric air-fuel mixture is burned. When the oxygen concentration is in the vicinity of the oxygen concentration of the gas, the oxidation-reduction reaction between unburned substances (HC, etc.) in the exhaust gas and nitrogen oxides (NOx) is promoted, and these are purified at a high purification rate. Can do.

  Hereinafter, the oxygen concentration of the exhaust gas is also referred to as “the air-fuel ratio of the exhaust gas”. The oxygen concentration of the exhaust gas is the oxygen concentration of the gas generated when the air-fuel mixture having the stoichiometric air-fuel ratio burns. Also referred to as “fuel ratio”. That is, the fact that the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio and the air-fuel ratio of the air-fuel mixture introduced into the combustion chamber are substantially the same. As described above, an air-fuel ratio smaller than the stoichiometric air-fuel ratio is also referred to as “rich air-fuel ratio”, and an air-fuel ratio greater than the stoichiometric air-fuel ratio is also referred to as “lean air-fuel ratio”.

  FIG. 2 is a schematic diagram showing the exhaust gas purification rate by the catalyst 53 when the temperature of the catalyst 53 is equal to or higher than the activation temperature. As shown in FIG. 2, when the air-fuel ratio A / F of the exhaust gas introduced into the catalyst 53 is an air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio stoich, nitrogen oxides (NOx) and unburned substances (HC) contained in the exhaust gas , CO) are most efficiently purified. On the other hand, as the air-fuel ratio A / F of the exhaust gas is separated from the stoichiometric air-fuel ratio stoich, the purification rate decreases.

  Here, regarding the degree of reduction (decrease rate) of the purification rate of nitrogen oxide (NOx), the catalyst 53 “same reduction when the air-fuel ratio A / F of the exhaust gas moves away from the stoichiometric air-fuel ratio stoich toward the lean side. The rate is larger than the rate of decrease when the air-fuel ratio A / F of the exhaust gas moves away from the stoichiometric air-fuel ratio stoich toward the rich side. In other words, the purification rate of nitrogen oxides (NOx) decreases significantly when the air-fuel ratio A / F of the exhaust gas moves away from the stoichiometric air-fuel ratio stoich toward the lean side, but the air-fuel ratio A / F is the same. However, in the case of deviating from the stoichiometric air-fuel ratio stoich toward the rich side, it does not decrease to an unacceptable level in terms of purifying nitrogen oxides (NOx).

  In the engine 10, the temperature of the catalyst 53 is acquired (estimated) based on the operating parameters of the engine 10. Details of the method for obtaining (estimating) the temperature of the catalyst 53 will be described later. Then, the temperature of the exhaust gas is controlled based on the acquired temperature Tcat of the catalyst 53.

  Referring to FIG. 1 again, an accelerator pedal 61 for inputting an acceleration request, a required torque and the like to the engine 10 is provided outside the engine 10. The accelerator pedal 61 is operated by an operator of the engine 10.

  Further, the various sensors 71 to 78 will be described in detail. The first device includes an intake air amount sensor 71, a throttle valve opening sensor 72, a cam position sensor 73, a crank position sensor 74, a water temperature sensor 75, an upstream air conditioner. A fuel ratio sensor 76, a downstream air-fuel ratio sensor 77, and an accelerator opening sensor 78 are provided.

  The intake air amount sensor 71 is provided in the intake passage (intake pipe 42). The intake air amount sensor 71 is configured to output a signal corresponding to an intake air amount that is a mass flow rate of air flowing through the intake pipe 42 (that is, a mass of air sucked into the engine 10). Based on this signal, a measured value of the intake air amount Ga is acquired.

  The throttle valve opening sensor 72 is provided in the vicinity of the throttle valve 44. The throttle valve opening sensor 72 is configured to output a signal corresponding to the opening of the throttle valve 44. Based on this signal, the throttle valve opening degree TA is acquired.

  The cam position sensor 73 is provided in the vicinity of the variable intake timing device 33. The cam position sensor 73 is configured to output a signal having one pulse every time the intake camshaft rotates 90 ° (that is, every time the crankshaft 24 rotates 180 °). Based on this signal, the rotational position (cam position) of the intake camshaft is acquired.

  The crank position sensor 74 is provided in the vicinity of the crankshaft 24. The crank position sensor 74 outputs a signal having a narrow pulse every time the crankshaft 24 rotates 10 °, and outputs a signal having a wide pulse every time the crankshaft 24 rotates 360 °. It is configured. Based on these signals, the number of rotations of the crankshaft 24 per unit time (hereinafter also simply referred to as “engine speed NE”) is acquired.

  The water temperature sensor 75 is provided in a cooling water passage that flows in the cylinder 21. The water temperature sensor 75 is configured to output a signal corresponding to the temperature of the cooling water. Based on this signal, the measured value of the coolant temperature THW is obtained.

  The upstream air-fuel ratio sensor 76 is provided in the exhaust passage on the upstream side of the catalyst 53 (in the vicinity of the collection portion of the exhaust manifold 51 or on the downstream side of the collection portion). The upstream air-fuel ratio sensor 76 is a known limit current type air-fuel ratio sensor. The upstream air-fuel ratio sensor 76 is configured to output an output value Vabyfs corresponding to the air-fuel ratio A / F of the exhaust gas introduced into the catalyst 53, as shown in FIG. Based on this output value Vabyfs, the air-fuel ratio of the exhaust gas introduced into the catalyst 53 is acquired.

  Hereinafter, the exhaust gas introduced into the catalyst 53 is also referred to as “catalyst introduction gas”. Further, hereinafter, the air-fuel ratio of the catalyst introduction gas is also referred to as “catalyst upstream air-fuel ratio abyfs”. In addition, hereinafter, the relationship between the output value Vabyfs and the air-fuel ratio A / F shown in FIG. 3 is also referred to as “table Mapabyfs”.

  The downstream air-fuel ratio sensor 77 is provided in the exhaust passage on the downstream side of the catalyst 53. The downstream air-fuel ratio sensor 77 is a known electromotive force type (concentration cell type) air-fuel ratio sensor. As shown in FIG. 4, the downstream side air-fuel ratio sensor 77 is configured to output an output value Voxs corresponding to the air-fuel ratio of the exhaust gas discharged from the catalyst 53. Based on this output value Voxs, the air-fuel ratio of the exhaust gas discharged from the catalyst 53 is acquired.

  Hereinafter, the exhaust gas discharged from the catalyst 53 is also referred to as “catalyst exhaust gas”. Further, hereinafter, the air-fuel ratio of the catalyst exhaust gas is also referred to as “catalyst downstream air-fuel ratio oxs”.

  Based on the catalyst upstream air-fuel ratio abyfs and the catalyst downstream air-fuel ratio oxs acquired as described above, the air-fuel ratio A / F of the air-fuel mixture supplied to the engine 10 is controlled.

  Referring again to FIG. 1, the accelerator opening sensor 78 is provided on the accelerator pedal 61. The accelerator opening sensor 78 is configured to output a signal corresponding to the opening of the accelerator pedal 61. Based on this signal, the accelerator pedal opening degree Accp is acquired.

Further, the engine 10 includes an electronic control device 80.
The electronic control unit 80 includes a CPU 81, a ROM 82 in which programs executed by the CPU 81, tables (maps), constants, and the like are stored in advance, a RAM 83 in which the CPU 81 temporarily stores data as necessary, and data in a state where power is turned on. And a backup RAM 84 that holds the stored data while the power is shut off, and an interface 85 including an AD converter. The CPU 81, ROM 82, RAM 83, RAM 84, and interface 85 are connected to each other via a bus.

The interface 85 is connected to the above-described sensors and is configured to transmit signals output from the sensors to the CPU 81. Further, the interface 85 is connected to the actuator 33a, the injector 34, the igniter 39, the throttle valve actuator 44a, and the like of the variable intake timing device 33, and is configured to send an instruction signal to them in response to an instruction from the CPU 81.
The above is the outline of the system in which the first device is applied to the engine 10.

<Outline of device operation>
Hereinafter, an outline of the operation of the first device will be described with reference to FIG. FIG. 5 is a schematic flowchart showing an outline of the operation of the first device.

  When air-fuel ratio control is being performed, the first device determines a fuel change amount DFaf1 for making the air-fuel ratio of the air-fuel mixture coincide with the target air-fuel ratio (the stoichiometric air-fuel ratio in this example) in step 310. To do. When the exhaust gas temperature control is started when the air-fuel ratio control is being performed, the first device determines “Yes” at step 320. In step 330, the first device determines a fuel change amount (fuel change amount DFaf4 by air-fuel ratio control and fuel change amount DFex4 by exhaust gas temperature control) when exhaust gas temperature control is performed.

  Specifically, the first device calculates the fuel change amount DFex4 by the exhaust gas temperature control and the fuel change amount DFaf4 by the air-fuel ratio control as “the sum of them (DFex4 + DFaf4) is before the exhaust gas temperature control is started. The fuel change amount (DFaf1 above) at the time or the time when the control is started (that is, the time before the control is started).

  Next, in step 360 after passing through step 340 and step 350, the first device adds the fuel change amounts DFex4 and DFaf4 determined as described above to the basic fuel injection amount Fbase, thereby obtaining the final fuel injection amount. Determine Fi. Then, in step 370, the first device causes the injector 34 to inject only the final fuel injection amount Fi from the injector 34.

If the exhaust gas temperature control is not performed, the first device determines “No” in step 320. In this case, as shown in step 380, the fuel change amount by the exhaust gas temperature control is zero. Then, in step 360 after passing through step 380 and step 350, the first device determines the final fuel injection amount Fi by adding only the fuel change amount DFaf1 by the air-fuel ratio control to the basic fuel injection amount Fbase. To do.
The above is the outline of the operation of the first device.

  Hereinafter, for convenience, the fuel change amount by air-fuel ratio control is also referred to as “air-fuel ratio related change amount DFaf”, and the fuel change amount by exhaust gas temperature control is also referred to as “exhaust gas temperature-related change amount DFex”. Further, the determination of the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex in accordance with the above-described concept is also referred to as a “first control method”.

<Air-fuel ratio control>
Next, the concept of air-fuel ratio control will be described.

  The air-fuel ratio control in the first device is performed in order to make the upstream air-fuel ratio (the air-fuel ratio of the catalyst introduction gas) abyfs obtained based on the output value Vabyfs of the upstream air-fuel ratio sensor 76 coincide with the upstream target air-fuel ratio abyfr. Main feedback control "and" sub feedback control "for making the output value Voxs of the downstream air-fuel ratio sensor 77 coincide with the downstream target output value Voxsref.

  More specifically, first, the output value Vabyfs of the upstream air-fuel ratio sensor 76 reduces the output deviation amount DVoxs, which is the difference between the output value Voxs of the downstream air-fuel ratio sensor 77 and the downstream target output value Voxsref. The sub-feedback amount Vafsfb calculated as described above is corrected. Next, the “feedback control output value Vabyfc” obtained by this correction is applied to the table Mapabyfs (see FIG. 3), whereby “feedback control air-fuel ratio (corrected detected air-fuel ratio) abyfsc” is calculated. The Then, the final fuel injection amount Fi is controlled such that the feedback control air-fuel ratio abyfsc matches the “upstream target air-fuel ratio abyfr”. Hereinafter, this air-fuel ratio control will be described in more detail.

  As will be described later, the “main feedback amount” calculated in connection with the main feedback control corresponds to the “air-fuel ratio related change amount DFaf” in the first device.

1. Main feedback control First, main feedback control will be described.
The first device calculates the feedback control output value Vabyfc (k) at the present time (time k) according to the following equation (1). In the following equation (1), Vabyfs represents the output value of the upstream air-fuel ratio sensor 76, and Vafsfb represents the sub-feedback amount calculated based on the output value Voxs of the downstream air-fuel ratio sensor 77. A method of calculating the sub feedback amount Vafsfb will be described later.

      Vabyfc (k) = Vabyfs (k) + Vafsfb (k) (1)

  Next, the first device applies the feedback control output value Vabyfc (k) to the table Mapabyfs (see FIG. 3) according to the following equation (2), so that the current air-fuel ratio for feedback control abyfsc (k ).

      abyfsc (k) = Mapabyfs (Vabyfc (k)) (2)

  Next, according to the following expression (3), the first device calculates the cylinder intake air amount Mc (k), which is the amount of air sucked into the cylinder at the current time, by the current upstream target air-fuel ratio abyfr (k). By dividing, the current basic fuel injection amount Fbase (k) is calculated. For example, the stoichiometric air-fuel ratio stoich is adopted as the upstream target air-fuel ratio abyfr (k).

      Fbase (k) = Mc (k) / abyfr (k) (3)

  The in-cylinder intake air amount Mc is calculated based on the intake air amount Ga and the engine rotational speed NE at that time each time an intake stroke is performed in each cylinder. For example, the in-cylinder intake air amount Mc is calculated by dividing a value obtained by subjecting the intake air amount Ga to the first-order lag processing by the engine speed NE. This in-cylinder intake air amount Mc is stored in the RAM 83 as data associated with each time point (time k−N,..., Time k−1, time k, time k + 1,...) When the intake stroke is performed. Stored in The in-cylinder intake air amount Mc may be calculated by a known intake air amount model (a model constructed based on the behavior of air in the intake passage).

  Next, the first device corrects the basic fuel injection amount Fbase (k) by a main feedback amount DFaf (k) described later according to the following equation (4) (the main feedback amount DFaf (k) is added to the basic fuel injection amount Fbase). The final fuel injection amount Fi (k) is calculated. Then, the first device injects fuel of the final fuel injection amount Fi (k) from the injector 34 of the cylinder in which the intake stroke is performed.

      Fi (k) = Fbase (k) + DFaf (k) (4)

  Thus, the main feedback amount DFaf is an amount determined so that the air-fuel ratio of the catalyst introduction gas (in other words, the air-fuel ratio of the air-fuel mixture) matches the target air-fuel ratio. That is, the main feedback amount corresponds to the “air-fuel ratio related change amount DFaf” described above.

  The main feedback amount DFaf (k) in the above equation (4) is calculated as follows. First, according to the following equation (5), the first device calculates the in-cylinder intake air amount Mc (k−N) at the time (time k−N) before the N cycle from the current time by using the feedback control air-fuel ratio (correction detection). By dividing by (air-fuel ratio) abyfsc (k), the “cylinder fuel supply amount Fc (k−N)”, which is the amount of fuel supplied to the combustion chamber 25 at a time N cycles before the current time, is calculated. .

      Fc (k−N) = Mc (k−N) / abyfsc (k) (5)

  In the above equation (5), the in-cylinder intake air amount Mc (k−N) N cycles before the present time is divided by the current feedback control air-fuel ratio abyfsc (k), so that N cycles before the current time. The in-cylinder fuel supply amount Fc (k−N) is calculated. This is because it takes time corresponding to N cycles until the air-fuel mixture combusted in the combustion chamber 25 reaches the upstream air-fuel ratio sensor 76.

  Next, according to the following equation (6), the first device calculates the cylinder intake air amount Mc (k−N) N cycles before the current time at the upstream target air-fuel ratio abyfr (k−N) N cycles before the current time. By dividing, “target in-cylinder fuel supply amount Fcr (k−N)” N cycles before the present time is calculated.

      Fcr (k−N) = Mc (k−N) / abyfr (k−N) (6)

  Next, the first device subtracts the in-cylinder fuel supply amount Fc (k−N) from the target in-cylinder fuel supply amount Fcr (k−N) according to the following equation (7). Deviation DFc (k) "is calculated.

      DFc (k) = Fcr (k−N) −Fc (k−N) (7)

  Next, the first device calculates the main feedback amount DFaf (k) according to the following equation (8). In the following equation (8), Gp represents a preset proportional gain, Gi represents a preset integral gain, K represents a predetermined coefficient, and SDFc represents an integral value of the in-cylinder fuel supply amount deviation DFc.

      DFaf (k) = (Gp · DFc (k) + Gi · SDFc (k)) · K (8)

As shown in the equations (7) and (8), the first device calculates the main feedback amount DFaf (k) by proportional-integral control based on the feedback control air-fuel ratio abyfsc and the upstream target air-fuel ratio abyfr. To do. Then, as shown in the above equation (4), the final fuel injection amount Fi (k) is calculated by adding the main feedback amount DFaf (k) thus calculated to the basic fuel injection amount Fbase.
The above is the main feedback control performed by the first device.

2. Sub-feedback control Next, sub-feedback control will be described.
The first device subtracts the current output value Voxs (k) of the downstream air-fuel ratio sensor 77 from the current downstream target output value Voxsref (k) according to the following equation (9), thereby obtaining the current output deviation amount. Calculate DVoxs (k). For example, the stoichiometric air-fuel ratio stoich is adopted as the downstream target output value Voxsref.

      DVoxs (k) = Voxsref (k) −Voxs (k) (9)

  Next, the first device calculates the sub feedback amount Vafsfb (k) at the current time according to the following equation (10). In the following equation (10), Kp represents a preset proportional gain (proportional constant), Ki represents a preset integral gain (integral constant), and SDVoxs represents an integral value of the output deviation amount DVoxs.

      Vafsfb (k) = Kp · DVoxs (k) + Ki · SDVoxs (k) (10)

As shown in the above equations (9) and (10), the first device calculates the sub feedback amount Vafsfb by proportional-integral control based on the output value Voxs of the downstream air-fuel ratio sensor 77 and the downstream target output value Voxsref. calculate. As shown in the above equation (1), the sub-feedback amount Vafsfb (k) calculated in this way is added to the output value Vabyfs (k) of the upstream air-fuel ratio sensor 76, whereby the feedback control output value Vabyfc (K) is calculated.
The above is the sub feedback control performed by the first device.

3. Summary of Air-Fuel Ratio Control As described above, the first device corrects the output value Vabyfs by adding the sub-feedback amount Vafsfb to the output value Vabyfs of the upstream air-fuel ratio sensor 76, and for feedback control obtained by this correction The feedback control air-fuel ratio abyfsc is calculated based on the output value Vabyfc (= Vabyfs + Vafsfb). Then, the first device calculates the fuel injection amount Fi so that the calculated feedback control air-fuel ratio abyfsc matches the upstream target air-fuel ratio abyfr. As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine 10 is matched with a predetermined target air-fuel ratio (for example, the stoichiometric air-fuel ratio stoich).
The above is the air-fuel ratio control performed by the first device.

<Exhaust gas temperature control>
Next, the concept of exhaust gas temperature control will be described.

  The exhaust gas temperature control in the first device is performed based on the “temperature (convergence temperature) Tf estimated that the temperature of the catalyst 53 will reach at a future time point” calculated based on the current operating state of the engine 10 and the convergence temperature Tf. And “estimated temperature (current temperature) Tp of the catalyst 53 at the current time point” calculated based on the above.

  More specifically, the first device has a convergence temperature table MapTf (NE (k), KL () that predetermines the “relationship between the engine rotational speed NE, the load factor KL, and the convergence temperature Tf of the catalyst 53”. k)) ”is applied to the current engine speed NE (k) and the load factor KL (k) to calculate the convergence temperature Tf (k) at the current time (time k).

  The convergence temperature table MapTf (NE (k), KL (k)) can be determined based on the results of experiments performed in advance. As is well known, the load factor KL is a value representing the load state of the engine 10, and is the maximum amount of gas that can be introduced into the combustion chamber 25 (for example, the total displacement of the engine 10 is the number of combustion chambers). It is a value representing the ratio of the amount of gas (actual amount) actually introduced into the combustion chamber 25 to the divided amount). For example, when the load factor is expressed as a percentage, the load factor when the actual amount matches the maximum amount is 100%, and the load factor when the actual amount is zero is zero%.

  Further, the first device calculates the current temperature Tp (k) according to the following equation (11). In the following equation (11), Tp (k) represents the current temperature at the present time, Tp (k−1) represents the current temperature at a time one cycle before the current time (time k−1), and P represents a predetermined coefficient. .

      Tp (k) = Tp (k−1) + {Tf−Tp (k−1)} / P (11)

  As understood from the above equation (11), the current temperature Tp is determined so as to gradually approach the convergence temperature Tf as time elapses. Further, as understood in the same manner, the current temperature Tp approaches the convergence temperature Tf in a shorter time as the coefficient P is smaller.

  The first device performs exhaust gas temperature control when “both” of the convergence temperature Tf (k) and the current temperature Tp (k) calculated as described above are equal to or higher than a predetermined threshold temperature Tcatth.

  More specifically, the first device is configured to determine the relationship between the engine rotational speed NE, the intake air amount Ga, and the exhaust gas temperature related change amount DFex in advance, the exhaust gas temperature related change amount table MapDFex (NE, Ga ) Is used to calculate the exhaust gas temperature related change amount DFex (k) at the present time by applying the engine speed NE (k) and the intake air amount Ga (k) at the current time. The exhaust gas temperature related variation amount DFex is determined as an appropriate value that can appropriately reduce the temperature of the exhaust gas.

  Then, the first device corrects the basic fuel injection amount Fbase (k) shown in the above equation (3) by the exhaust gas temperature related change amount DFex (k) according to the following equation (12) (basic fuel injection amount Fbase (k ) Is added to the exhaust gas temperature related variation amount DFex (k)) to calculate the final fuel injection amount Fi (k).

      Fi (k) = Fbase (k) + DFex (k) (12)

Thus, when the convergence temperature Tf and the current temperature Tp of the catalyst 53 satisfy the predetermined conditions, the first device corrects the basic fuel injection amount Fbase so as to increase by the exhaust gas temperature related change amount DFex. Thereby, the temperature of exhaust gas is appropriately reduced according to the operating state of the engine 10 due to the fuel cooling effect.
The above is the exhaust gas temperature control performed by the first device.

  As understood from the air-fuel ratio control and exhaust gas temperature control described above (particularly, the equations (4) and (12)), when both of the exhaust gas temperature control and the air-fuel ratio control are performed simultaneously, The first device corrects the basic fuel injection amount Fbase (k) by the air / fuel ratio related change amount DFaf (k) and the exhaust gas temperature related change amount DFex according to the following equation (13) (the basic fuel injection amount Fbase is related to the air / fuel ratio): The final fuel injection amount Fi (k) is calculated by adding the change amount DFaf and the exhaust gas temperature related change amount DFex).

      Fi (k) = Fbase (k) + DFaf (k) + DFex (k) (13)

<Example of control by first control method>
The first device performs the above-described air-fuel ratio control and exhaust gas temperature control in accordance with the “first control method”. Hereinafter, an example in which air-fuel ratio control and exhaust gas temperature control (both or one) are performed will be described with reference to FIGS. 6 and 7. FIG. 6 is a time chart showing an example (reference example) when the first device “does not perform” control according to the first control method, and FIG. 7 shows the first device according to the first control method. It is a time chart which shows the example in the case of carrying out control. 6 and 7 show waveforms in which the actual waveform of each value is schematically shown for easy understanding. 6 and 7 are time charts on the premise that the air-fuel ratio related variation amount DFaf is a positive value when the air-fuel ratio control is being performed.

1. When control according to the first control method is not performed (reference example)
At time ta in the time chart shown in FIG. 6, “only air-fuel ratio control” of air-fuel ratio control and exhaust gas temperature control is performed.

  At time ta, the intake air amount Ga is the value Ga1. On the other hand, regarding the temperature Tcat of the catalyst 53, the engine speed NE and the load factor KL, which are parameters related to the intake air amount Ga, are applied to the convergence temperature table MapTf (NE, KL), so that the catalyst 53 at the time ta. The convergence temperature Tf (solid line in the figure) is calculated. At time ta, the convergence temperature Tf is the value Tf1. This value Tf1 is lower than the threshold temperature Tcatth. Further, the convergence temperature Tf is applied to the above equation (11), whereby the current temperature Tp of the catalyst 53 (broken line in the figure) is calculated. At time ta, the current temperature Tp is lower than the threshold temperature Tcatth.

  At time ta, the air-fuel ratio related variation amount DFaf determined according to the air-fuel ratio control described above is the value a. On the other hand, since the exhaust gas temperature control is not performed at time ta, the exhaust gas temperature related variation amount DFex is zero. Therefore, at time ta, the sum DFaf + DFex of the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex is the value a.

  At time ta, the target air-fuel ratio A / Ftgt (synonymous with upstream target air-fuel ratio abyfr) of the air-fuel mixture is set to the stoichiometric air-fuel ratio stoich. In this example, the actual air-fuel ratio A / F at time ta coincides with the theoretical air-fuel ratio stoich that is the target air-fuel ratio. Note that the value a of the air-fuel ratio related variation amount DFaf described above is determined so that the actual air-fuel ratio (actual air-fuel ratio) A / F matches this target air-fuel ratio (theoretical air-fuel ratio stoich).

  As described above, the catalyst 53 can efficiently purify the exhaust gas when the air-fuel ratio of the exhaust gas (synonymous with the air-fuel ratio of the air-fuel mixture) is the stoichiometric air-fuel ratio. In particular, paying attention to nitrogen oxides (NOx) contained in the exhaust gas, since the air-fuel ratio of the air-fuel mixture at the time ta is the stoichiometric air-fuel ratio stoich, the nitrogen oxides (NOx) contained in the gas discharged from the engine 10 Is a value near zero. Hereinafter, the amount of nitrogen oxides contained in the gas discharged from the engine 10 is also referred to as “NOx emission amount”.

  Thereafter, at time tb, the intake air amount Ga increases from the value Ga1 to the value Ga2. At this time, the convergence temperature Tf related to the intake air amount Ga also increases from the value Tf1 to the value Tf2. The value Tf2 is higher than the threshold temperature Tcatth. On the other hand, the current temperature Tp rises so as to gradually approach the convergence temperature Tf2 according to the above equation (11) (that is, it does not change abruptly), so it is a value near the value Tf1 at time tb.

  At time tb, as described above, the air-fuel ratio related variation amount DFaf is the value a, and the exhaust gas temperature related variation amount DFex is zero. Actually, since the intake air amount Ga is changed at time tb, the air-fuel ratio related change amount DFaf may increase in order to keep the air-fuel ratio of the air-fuel mixture at the stoichiometric air-fuel ratio stoich. However, in this example, it is assumed that the magnitude of the air-fuel ratio related variation amount DFaf does not substantially change before and after the time tb for easy understanding.

  Thereafter, the current temperature Tp increases as time passes, and becomes equal to or higher than the threshold temperature Tcatth at time tc. That is, at time tc, “both” of the convergence temperature Tf and the current temperature Tp are equal to or higher than the threshold temperature Tcatth. At this time, in this example, the air-fuel ratio control is “stopped” and the exhaust gas temperature control is “started”.

  As a result, at time tc, the air-fuel ratio related variation amount DFaf decreases from the value a to zero, and the exhaust gas temperature related variation amount DFex increases from zero to the value b. Therefore, the total DFaf + DFex changes from the value a to the value b at time tc.

  In this example, it is assumed that the value b is smaller than the value a. According to this assumption, the total DFaf + DFex (value b) at time tc is smaller than the total DFaf + DFex (value a) at a time point before time tc (for example, time ta, time tb, or time tc). Become. Therefore, at the time tc, the actual air-fuel ratio A / F changes to a value (lean side value) larger than the stoichiometric air-fuel ratio stoich. Note that since the air-fuel ratio control is stopped at time tc, the target air-fuel ratio A / Ftgt is not set (see the broken line in the figure).

  As a result, at the time tc, the air-fuel ratio of the exhaust gas also becomes a leaner air-fuel ratio than the stoichiometric air-fuel ratio stoich. Therefore, the fuel cooling effect cannot be obtained properly, and the temperature of the exhaust gas is not lowered appropriately. Furthermore, as described above, when the air-fuel ratio of the exhaust gas moves away from the stoichiometric air-fuel ratio stoich toward the lean side, the nitrogen oxide (NOx) purification efficiency is significantly reduced. Therefore, the NOx emission amount increases at time tc. Thereafter, during a period in which the intake air amount Ga is the value Ga2 (for example, at time td), the state in which the NOx emission amount is increased continues.

  Thereafter, at time te, the intake air amount Ga decreases from the value Ga2 to the value Ga1. At this time, the convergence temperature Tf decreases from the value Tf2 to the value Tf1, and the current temperature Tp decreases so as to gradually approach the convergence temperature Tf1.

  The current temperature Tp is lower than the threshold temperature Tcatth at time tf. That is, at the time tf, both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth. At this time, the exhaust gas temperature control is “finished” and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is “restarted”.

  As a result, at time tf, the air-fuel ratio related variation amount DFaf increases from zero to the value a, and the exhaust gas temperature related variation amount DFex decreases from the value b to zero. Therefore, at time tf, the total DFaf + DFex changes from the value b to the value a. As a result, the actual air-fuel ratio A / F matches the stoichiometric air-fuel ratio stoich, and the NOx emission amount decreases to a value near zero.

  Thus, when the control according to the first control method is not performed, the temperature of the exhaust gas may not be appropriately reduced during the period when the exhaust gas temperature control is performed. Furthermore, the NOx emission amount may increase during the period.

2. When Control According to the First Control Method is Performed At time ta in the time chart shown in FIG. 7, “air-fuel ratio control only” of air-fuel ratio control and exhaust gas temperature control is performed as described above.

  At the time ta, as described above, the intake air amount Ga is the value Ga1, and the convergence temperature Tf and the current temperature Tp are both lower than the threshold temperature Tcatth. Further, at time ta, the target air-fuel ratio A / Ftgt is set to the stoichiometric air-fuel ratio stoich, and the air-fuel ratio related variation amount DFaf is the value a. Further, the exhaust gas temperature related variation amount DFex is zero. Therefore, the total DFaf + DFex is the value a. At time ta, the actual air-fuel ratio A / F matches the target air-fuel ratio (theoretical air-fuel ratio stoich). As a result, the NOx emission amount is a value near zero.

  Thereafter, the intake air amount Ga increases from the value Ga1 to the value Ga2 at the time tb, and both the convergence temperature Tf and the current temperature Tp become equal to or higher than the threshold temperature Tcatth at the time tc.

  At this time, as described above, the total DFaf + DFex (value b) at time tc is smaller than the total DFaf + DFex (value a) at a time point before time tc (for example, time ta, time tb, or time tc). . Therefore, in this example, unlike the case where the control according to the first control method described above is not performed, the air-fuel ratio control is “continued” and the exhaust gas temperature control is started.

  As a result, at time tc, for example, the air-fuel ratio related change amount DFaf changes from the value a to the value c, and the exhaust gas temperature related change amount DFex changes from zero to the value b. Therefore, at time tc, the total DFaf + DFex changes from the value a to the value b + c.

  Here, the magnitude of the air-fuel ratio related variation amount DFaf (value c) varies depending on the basic fuel injection amount Fbase (see the description of the main feedback amount above) determined in relation to the target air-fuel ratio A / Ftgt. . Therefore, if it is assumed that the basic fuel injection amount Fbase does not change significantly before and after time tb (for example, in a steady state where the operating state of the engine 10 does not substantially change), the magnitude of the value c is the value a. Can be considered substantially the same. According to this assumption, the total DFaf + DFex (value b + c) at time tc is larger than value a. Therefore, at time tc, the actual air-fuel ratio A / F becomes a value (rich side value) smaller than the stoichiometric air-fuel ratio stoich.

  As a result, at time tc, the air-fuel ratio of the exhaust gas also becomes richer than the stoichiometric air-fuel ratio stoich. Therefore, a fuel cooling effect is appropriately obtained, and the temperature of the exhaust gas is appropriately reduced. Furthermore, as described above, even if the air-fuel ratio of the exhaust gas departs from the stoichiometric air-fuel ratio stoich toward the rich side, the NOx purification rate does not decrease to an unacceptable level. Therefore, at the time tc, the NOx emission amount is substantially maintained at a value near zero.

  The target air-fuel ratio A / Ftgt at time tc is appropriately set to an air-fuel ratio (rich air-fuel ratio) that is smaller than the target air-fuel ratio (theoretical air-fuel ratio stoich) before time tc.

  Thereafter, as described above, the intake air amount Ga decreases from the value Ga2 to the value Ga1 at the time te, and both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth at the time tf. At this time, the exhaust gas temperature control is ended, and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is continued.

Thus, when the control according to the first control method of the present invention is performed, the temperature of the exhaust gas can be appropriately reduced even during the period in which the exhaust gas temperature control is performed. Furthermore, it is possible to prevent the NOx emission amount from increasing even during the same period.
The above is an example of control by the first control method.

<Actual operation>
Hereinafter, the actual operation of the first device will be described.
In the first device, the CPU 81 performs FIG. 8 regarding the control of fuel injection, FIG. 9 regarding the calculation of the exhaust gas temperature related change amount, FIG. 10 regarding the calculation of the main feedback amount, and FIG. 11 regarding the calculation of the sub feedback amount. The routines shown in (1) and (2) are repeatedly executed at predetermined timings. Hereinafter, each routine executed by the CPU 81 will be described.

  First, the CPU 81 displays the “first” shown in the flowchart of FIG. 8 at each timing when the crank angle of an arbitrary cylinder coincides with a predetermined crank angle before the intake stroke (for example, 90 ° crank angle before exhaust top dead center) θf. The “fuel injection control routine” is repeatedly executed. With this routine, the CPU 81 determines the final fuel injection amount Fi in consideration of the air-fuel ratio related change amount DFaf and the exhaust gas temperature related change amount DFex, and causes the injector 34 to inject fuel only from the final fuel injection amount Fi. Hereinafter, for convenience, the cylinder before the intake stroke whose crank angle coincides with the predetermined crank angle θf is also referred to as “fuel injection cylinder”.

  Specifically, the CPU 81 starts the process from step 800 of FIG. 8 at the above timing and proceeds to step 810, where “the intake air amount Ga, the engine speed NE, the upstream target air-fuel ratio abyfr, By applying the intake air amount Ga (k) and the engine speed NE (k) at the current time (time k) to the target air / fuel ratio table Mapabyfr (Ga, NE) that predetermines the relationship of Determine abyfr (k).

  The upstream target air-fuel ratio abyfr is set to an air-fuel ratio (an air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio stoich) at which the catalyst 53 can efficiently purify the exhaust gas. For example, as the target air-fuel ratio abyfr, a stoichiometric air-fuel ratio stoich, an air-fuel ratio slightly richer than the stoichiometric air-fuel ratio stoich, or the like is adopted. As described above, the fact that the air-fuel ratio of the catalyst introduction gas is the stoichiometric air-fuel ratio stoich and that the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio stoich are substantially synonymous.

  Next, the CPU 81 proceeds to step 820. In step 820, the CPU 81 determines whether or not the exhaust gas temperature related change amount DFex (k) is zero (that is, whether or not exhaust gas temperature control is being performed). The setting of the exhaust gas temperature related change amount DFex will be described later (see the routine of FIG. 9).

  When the exhaust gas temperature related change amount DFex (k) at the present time is zero (that is, when the exhaust gas temperature control is not performed), the CPU 81 determines “Yes” in step 820 and proceeds to step 830.

  Next, the CPU 81 executes the processing of step 830 to step 850 in this order. The processing executed in steps 830 to 850 is as follows.

Step 830: The CPU 81 acquires an in-cylinder intake air amount Mc (k) that is an amount of air sucked into the fuel injection cylinder based on the intake air amount Ga (k) and the engine speed NE (k).
Step 840: The CPU 81 calculates the basic fuel injection amount Fbase (k) according to the above equation (3).
Step 850: The CPU 81 converts the basic fuel injection amount Fbase (k) into the air-fuel ratio related change amount DFaf (k) and the exhaust gas temperature related change amount DFex (k) according to the above equations (4), (12) and (13). ), The final fuel injection amount Fi (k) is calculated.

  After executing the processing of step 850, the CPU 81 proceeds to step 860, and determines whether or not “a condition for performing fuel cut control in which the fuel injection amount is zero (fuel cut control condition)” is satisfied. More specifically, the CPU 81 determines in step 860 that the fuel cut control condition is satisfied when both of the following conditions a-1 and a-2 are satisfied. In other words, the CPU 81 determines that the fuel cut control condition is not satisfied when at least one of the following conditions a-1 and a-2 is not satisfied.

(A-1) The accelerator pedal opening degree Accp is zero, or the throttle valve opening degree TA is zero.
(A-2) The engine speed NE is equal to or higher than a predetermined threshold value.

  The condition a-1 is a condition provided for determining whether or not the magnitude of torque required for the engine 10 is sufficiently small. The predetermined threshold value in the condition a-2 is set to an appropriate value that can be determined that the operation of the engine 10 is continued even if the fuel injection amount is zero.

  If the fuel cut control condition is not satisfied at the present time, the CPU 81 makes a “No” determination at step 860 to proceed to step 870. In step 870, the CPU 81 gives an instruction to the injector 34 provided in the fuel injection cylinder so as to inject the fuel of the final fuel injection amount Fi (k). Thereafter, the CPU 81 proceeds to step 895 to end the present routine tentatively. Thereby, the fuel of the final fuel injection amount Fi (k) calculated by the above-described processes is injected into the fuel injection cylinder.

  On the other hand, when the fuel cut control condition is “satisfied” at the present time, the CPU 81 determines “Yes” in step 860 and proceeds to step 880. In step 880, the CPU 81 stores zero as the value of the final fuel injection amount Fi (k). As a result, even if an instruction to inject the fuel of the final fuel injection amount Fi (k) is made in step 870 following step 880, no fuel is injected. Thereby, the fuel cut operation in which the fuel injection amount is zero is executed.

  Next, the CPU 81 repeatedly executes the “first exhaust gas temperature related change amount calculation routine” shown by the flowchart in FIG. 9 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θf. By this routine, the CPU 81 calculates the convergence temperature Tf and the current temperature Tp of the catalyst 53, and calculates the exhaust gas temperature related change amount DFex.

  More specifically, the CPU 81 starts the process from step 900 in FIG. 9 at the above timing and proceeds to step 910. In the “convergence temperature table MapTf (NE, KL)” described above, the current engine speed NE ( The convergence temperature Tf (k) of the catalyst 53 is calculated by applying k) and the load factor KL (k).

  Next, the CPU 81 proceeds to step 920. In step 920, the CPU 81 calculates the current temperature Tp (k) based on the convergence temperature Tf (k) according to the above equation (11). The coefficient P in the above equation (11) is set to an appropriate value considering the heat capacity of the catalyst 53 and the like.

  Next, the CPU 81 proceeds to step 930. In step 930, the CPU 81 determines whether or not to perform exhaust gas temperature control at the present time. Specifically, the CPU 81 determines whether or not the convergence temperature Tf (k) and the current temperature Tp (k) satisfy both of the following conditions b-1 and b-2. In the following conditions b-1 and b-2, Tcatth represents a predetermined threshold temperature.

(B-1) The convergence temperature Tf (k) is equal to or higher than the threshold temperature Tcatth.
(B-2) The current temperature Tp (k) is equal to or higher than the threshold temperature Tcatth.

  In the above conditions b-1 and b-2, the threshold temperature Tcatth is a value determined in consideration of the heat resistance of the catalyst 53, and both the convergence temperature Tf and the current temperature Tp are equal to or higher than the threshold temperature Tcatth. Further, the exhaust gas purification performance of the catalyst 53 is set to an appropriate value that can be determined to be deteriorated.

  If at least one of the above conditions b-1 and b-2 is not satisfied at the present time, the CPU 91 determines “No” in step 930 and proceeds to step 940 to set the exhaust gas temperature related change amount DFex (k) to zero. Store. Thereafter, the CPU 81 proceeds to step 995 to end the present routine tentatively.

  As described above, when at least one of the conditions b-1 and b-2 is not satisfied, the value of the exhaust gas temperature related variation amount DFex for correcting the basic fuel injection amount Fbase is set to zero. That is, in this case, the fuel change amount for reducing the temperature of the exhaust gas is not corrected (see step 850 in FIG. 8). Thus, when the exhaust gas temperature control is not performed, the value of the exhaust gas temperature related variation amount DFex is set to zero.

  On the other hand, if both of the above conditions b-1 and b-2 are satisfied at the present time, the CPU 91 determines “Yes” in step 930 and proceeds to step 950. In step 950, the CPU 81 applies the current engine speed NE (k) and the intake air amount Ga (k) to the above-described “exhaust gas temperature related change amount table MapDFex (NE, Ga)”. The exhaust gas temperature related change amount DFex (k) is calculated.

  By the way, the CPU 81 stores the time (for example, time k) when the result of determination in step 930 changes from “No” to “Yes” in the RAM 83 as the reference time kref. This reference time point kref is when a new reference time point kref is stored in the RAM 83 at a future time point (when the determination result at Step 930 changes from “No” to “Yes” again at a future time point). The new reference time point kref is overwritten (updated). In other words, the reference time point kref is held in the RAM 83 until it is overwritten by a new reference time point kref.

  Thereafter, the CPU 81 proceeds to step 995 to end the present routine tentatively. As described above, when both the conditions b-1 and b-2 are satisfied, the value of the exhaust gas temperature related change amount DFex is calculated. Then, the basic fuel injection amount Fbase is corrected by this value (see step 850 in FIG. 8).

  Further, the CPU 81 is a flowchart shown in FIG. 10 at each timing when the crank angle of the fuel injection cylinder coincides with a predetermined crank angle θg before the intake stroke (for example, an angle advanced by a predetermined amount from the crank angle θf). The “first air-fuel ratio related change amount (main feedback amount) calculation routine” shown in FIG. The CPU 81 calculates the air-fuel ratio related change amount DFaf by this routine.

  As described above, the air-fuel ratio related variation amount DFaf corresponds to the main feedback amount in the above equations (1) to (13). Therefore, hereinafter, for convenience, the air-fuel ratio related change amount is also referred to as “main feedback amount”.

  The routine of FIG. 10 will be specifically described. The CPU 81 starts the process from step 1000 of FIG. 10 at the above timing, and proceeds to step 1005 to “match the catalyst upstream air-fuel ratio abyfs with the upstream target air-fuel ratio abyfr. It is determined whether or not a “condition for performing feedback control to be performed (main feedback control condition)” is satisfied. More specifically, the CPU 81 determines in step 1005 that the main feedback control condition is satisfied when all of the following conditions c-1 to c-5 are satisfied. In other words, the CPU 81 determines that the main feedback control condition is not satisfied when at least one of the following conditions c-1 to c-5 is not satisfied.

(Condition c-1) The catalyst temperature Tcat is equal to or higher than a predetermined activation temperature.
(Condition c-2) The coolant temperature THW is equal to or higher than a predetermined threshold.
(Condition c-3) The intake air amount Ga is equal to or less than a predetermined threshold value.
(Condition c-4) The upstream air-fuel ratio sensor 76 is activated.
(Condition c-5) The fuel cut operation (operation in which the final fuel injection amount Fi is zero) is not being executed.

  The activation temperature in the condition c-1 is set to an appropriate value at which it can be determined that the catalyst 53 is activated. The threshold value in the condition c-2 is set to an appropriate value that can be determined that the engine 10 has been warmed up. The threshold value in the condition c-3 is set to an appropriate value that can be determined that the load on the engine 10 is not excessively large. The condition c-4 is a condition that is provided because the output value Vabyfs of the upstream air-fuel ratio sensor 76 is used in the main feedback control. Condition c-5 is a condition that is provided because the fuel injection amount Fi cannot be changed during the fuel cut operation.

  If the main feedback control condition is “satisfied” at the present time, the CPU 81 makes a “Yes” determination at step 1005 to proceed to step 1010. In step 1010, the CPU 81 determines whether or not the exhaust gas temperature related change amount DFex (k) is zero (that is, whether or not exhaust gas temperature control is being performed).

  When the exhaust gas temperature related change amount DFex (k) at the present time is zero (that is, when the exhaust gas temperature control is not performed), the CPU 81 determines “Yes” in step 1010. Next, the CPU 81 executes the processing of step 1015 to step 1045 following step 1010 in this order. The processing executed in steps 1015 to 1045 is as follows.

Step 1015: The CPU 81 calculates the feedback control output value Vabyfc (k) according to the above equation (1). The sub feedback amount Vafsfb (k) at the present time is calculated in a routine shown in FIG.
Step 1020: The CPU 81 determines the feedback control air-fuel ratio abyfsc (k) according to the above equation (2).
Step 1025: The CPU 81 calculates the in-cylinder fuel supply amount Fc (k−N) at a time point N cycles before the current time according to the above equation (5).
Step 1030: The CPU 81 calculates the target in-cylinder fuel supply amount Fcr (k−N) at a time point N cycles before the current time according to the above equation (6).
Step 1035: The CPU 81 calculates the in-cylinder fuel supply amount deviation DFc (k) according to the above equation (7).
Step 1040: The CPU 81 calculates the main feedback amount DFaf (k) according to the above equation (8). In the first device, “1” is adopted as the coefficient K. The integral value SDFc (k) of the in-cylinder fuel supply amount deviation DFc is a value obtained by integrating the values of the in-cylinder fuel supply amount deviation DFc up to the present time (see step 1045 below).
Step 1045: The CPU 81 adds the in-cylinder fuel supply amount deviation DFc (k) to the integrated value SDFc (k−1) of the in-cylinder fuel supply amount deviation DFc up to the present time, thereby obtaining a new in-cylinder fuel supply amount deviation. The integral value SDFc (k) of is calculated (updated).

  After executing the processing of step 1045, the CPU 81 proceeds to step 1095 to end the present routine tentatively.

  By each process described above, the main feedback amount DFaf (k) is calculated by proportional integral control. Then, the final fuel injection amount Fi (k) is corrected using the main feedback amount DFaf (k) (see step 850 in FIG. 8). Since the exhaust gas temperature control is not performed at this time (determined as “Yes” in Step 1010), the final fuel injection amount Fi (k) is corrected only by the main feedback amount DFaf (k).

  On the other hand, when the exhaust gas temperature related variation amount DFex (k) is not zero at the present time (that is, when exhaust gas temperature control is performed), the CPU 81 makes a “No” determination at step 1010 and proceeds to step 1050. .

  In step 1050, the CPU 81 determines whether or not the exhaust gas temperature related variation amount DFex (k) at the current time is smaller than the main feedback amount DFaf (kref) at the reference time kref.

  If the exhaust gas temperature related change amount DFex (k) at the current time is equal to or larger than the main feedback amount DFaf (kref) at the reference time kref, the CPU 81 makes a “No” determination at step 1050 to proceed to step 1055. In step 1055, the CPU 81 stores zero in the main feedback amount DFaf (k), and proceeds to step 1060. In step 1060, the CPU 81 stores zero in the integral value SDFc (k) of the in-cylinder fuel supply amount deviation DFc. Thereafter, the CPU 81 proceeds to step 1095 to end the present routine tentatively.

  Thus, when exhaust gas temperature control is performed (DFex (k) is not zero) and the exhaust gas temperature related variation amount DFex (k) is equal to or greater than the air / fuel ratio related variation amount DFaf (kref), the The fuel ratio related variation amount DFaf is set to zero. Therefore, the “correction of the basic fuel injection amount Fbase by the main feedback amount DFaf (k)” described above is not performed (see step 850 in FIG. 8). That is, air-fuel ratio control is not performed.

  On the other hand, if the exhaust gas temperature related change amount DFex (k) at the current time is smaller than the main feedback amount DFaf (kref) at the reference time point kref, the CPU 81 determines “Yes” in step 1050, and the same as above. The processing of 1015 to step 1045 is executed in this order, and the routine proceeds to step 1095 to end the present routine tentatively.

  Thus, even if the exhaust gas temperature control is performed, the air-fuel ratio control is performed when the exhaust gas temperature-related change amount DFex (k) is smaller than the air-fuel ratio related change amount DFaf (kref). That is, both air-fuel ratio control and exhaust gas temperature control are performed (see step 850 in FIG. 8).

  When both the air-fuel ratio control and the exhaust gas temperature control are performed, the CPU 81 makes a “No” determination at step 820 in FIG. 8 and proceeds to step 890. In step 890, the CPU 81 stores “the air-fuel ratio abyfrsmall smaller than the upstream target air-fuel ratio at the reference time point kref” in the upstream target air-fuel ratio abyfr (k). Thus, in this case, the upstream target air-fuel ratio abyfr (k) is changed to the air-fuel ratio abyfrsmall. The air-fuel ratio abyfrsmall is set to an appropriate value in consideration of the exhaust gas temperature related variation amount DFex and the like.

  Incidentally, when the main feedback control condition is not satisfied at the present time, the CPU 81 determines “No” in step 1005 of FIG. Then, the CPU 81 proceeds to step 1095 via step 1055 and step 1060, and once ends this routine. As a result, the main feedback amount DFaf (k) is set to zero. Therefore, in this case, air-fuel ratio control is not performed.

  Next, the CPU 81 is a flowchart shown in FIG. 11 at each timing when the crank angle of the fuel injection cylinder coincides with a predetermined crank angle θh before the intake stroke (for example, an angle advanced by a predetermined amount from the crank angle θg). The “first sub feedback amount calculation routine” indicated by is repeatedly executed. The CPU 81 calculates the sub feedback amount Vafsfb by this routine.

  Specifically, the CPU 81 starts the processing from step 1100 in FIG. 11 at the above timing and proceeds to step 1110, and “makes the output value Voxs of the downstream air-fuel ratio sensor 77 coincide with the downstream target output value Voxsref. It is determined whether or not a “condition for performing sub-feedback control (sub-feedback control condition)” is satisfied. More specifically, in step 1110, the CPU 81 determines that the sub feedback control condition is satisfied when all of the following conditions d-1 to d-3 are satisfied. In other words, the CPU 81 determines that the sub feedback control condition is not satisfied when at least one of the following conditions d-1 to d-3 is not satisfied.

(Condition d-1) The main feedback condition is satisfied.
(Condition d-2) The upstream target air-fuel ratio abyfr is set to the stoichiometric air-fuel ratio stoich.
(Condition d-3) The downstream air-fuel ratio sensor 77 is activated.

  The condition d-1 is a condition provided for the sub feedback control to be executed in parallel with the main feedback control. The condition d-2 is a condition provided in consideration of the characteristic of the output value of the downstream air-fuel ratio sensor 77 (see FIG. 4). The condition d-3 is a condition that is provided because the output value Voxs of the downstream air-fuel ratio sensor 77 is used in the sub feedback control.

  If the sub-feedback control condition is satisfied at the current time point, the CPU 81 determines “Yes” in step 1110, and executes the processing of step 1120 to step 1140 following step 1110 in this order. The processing executed in steps 1120 to 1140 is as follows.

Step 1120: The CPU 81 calculates an output deviation amount DVoxs (k) according to the above equation (9). In the first device, in consideration of the exhaust gas purification performance of the catalyst 53, an output value corresponding to an air-fuel ratio slightly richer than the theoretical air-fuel ratio is adopted as the downstream target output value Voxsref.
Step 1130: The CPU 81 calculates the sub feedback amount Vafsfb (k) according to the above equation (10).
Step 1140: The CPU 81 calculates a new output deviation amount integrated value SDVoxs (k) by adding the output deviation amount DVoxs (k) to the integrated value SDVoxs (k−1) of the output deviation amount up to the present time ( Update.

  After executing the processing of step 1140, the CPU 81 proceeds to step 1195 to end the present routine tentatively.

  Through the above-described processes, the sub feedback amount Vafsfb (k) is calculated by proportional-integral control (see step 1130). Then, the output value Vabyfs (k) of the upstream air-fuel ratio sensor 76 is corrected using the sub feedback amount Vafsfb (k) (see step 1015 in FIG. 10). Further, a main feedback amount DFaf (k) is calculated based on the corrected feedback control output value Vabyfc (k) (see step 1040 in FIG. 10), and this main feedback amount DFaf (k) is used. Thus, the final fuel injection amount Fi (k) is corrected (see step 850 in FIG. 8).

  On the other hand, if the sub feedback control condition is not satisfied at the present time, the CPU 81 makes a “No” determination at step 1110 to proceed to step 1150. In step 1150, the CPU 81 stores zero in the sub feedback amount Vafsfb (k). Next, the CPU 81 proceeds to step 1160. In step 1160, the CPU 81 stores zero in the integrated value SDVoxs (k) of the output deviation amount. Thereafter, the CPU 81 proceeds to step 1195 to end the present routine tentatively.

  Thus, when the sub feedback control condition is not satisfied, the sub feedback amount Vafsfb is set to zero. Therefore, in this case, the output value Vabyfs of the upstream air-fuel ratio sensor 76 is not corrected by the sub feedback amount Vafsfb (see step 1015 in FIG. 10).

  As described above, the first device performs the exhaust gas temperature control when both the convergence temperature Tf and the current temperature Tp of the catalyst 53 are equal to or higher than the threshold temperature Tcatth (that is, calculates the exhaust gas temperature related change amount DFex). At the same time, the base fuel injection amount Fbase is corrected by the change amount DFex.) At this time, when the exhaust gas temperature related change amount DFex (k) is smaller than the air fuel ratio related change amount DFaf (kref) at the reference time point kref, the first device performs both the exhaust gas temperature control and the air fuel ratio control. As a result, the exhaust gas temperature related change amount DFex (k) and the air / fuel ratio related change amount DFaf (k) at the present time are equal to or greater than the air fuel ratio related change amount DFaf (kref) at the reference time point kref. A change amount DFex (k) and an air-fuel ratio related change amount DFaf (k) are determined.

  As a result, the amount of fuel in the period when the exhaust gas temperature control is performed is larger than the amount of fuel before the exhaust gas temperature control is performed. Therefore, a fuel cooling effect is appropriately obtained, and the temperature of the exhaust gas is appropriately reduced. Furthermore, since the air-fuel ratio of the catalyst introduction gas during the period in which the exhaust gas temperature control is performed is a richer value than the stoichiometric air-fuel ratio stoich, the NOx emission amount is substantially maintained at a value near zero. Thus, the 1st apparatus can achieve the objective of exhaust gas temperature control and air fuel ratio control appropriately as much as possible.

As can be understood from the above description, the first device follows the above routines regardless of whether the air-fuel ratio related variation amount DFaf (kref) at the reference time point kref is a positive value or a negative value. An appropriate air-fuel ratio related change amount DFaf and exhaust gas temperature related change amount DFex can be determined.
The above is the description of the first embodiment of the present invention.

(Second Embodiment)
Next, a control device (hereinafter also referred to as “second device”) according to a second embodiment of the present invention will be described.

<Outline of device>
The second device is applied to an engine having a configuration similar to that of the engine 10 to which the first device is applied (see FIG. 1, hereinafter referred to as “the engine 10” for convenience). Therefore, the description of the outline of the device to which the second device is applied is omitted.

<Outline of device operation>
The second device is different from the first device in that “the upstream target air-fuel ratio abyfr is determined in consideration of the exhaust gas temperature related variation amount DFex” when both exhaust gas temperature control and air-fuel ratio control are performed.

  More specifically, when the exhaust gas temperature related change amount DFex (k) is determined, the second device is “the sum of the exhaust gas temperature related change amount DFex (k) and the basic fuel injection amount Fbase (k). A value obtained by dividing by the basic fuel injection amount Fbase (k) is calculated. Further, the second device employs “a value obtained by dividing the upstream target air-fuel ratio abyfr (kref) at the reference time point kref by the calculated value” as the upstream target air-fuel ratio abyfr (k).

The second device performs air-fuel ratio control according to the upstream target air-fuel ratio abyfr (k) thus determined, and performs exhaust gas temperature control in the same manner as the first device.
The above is the outline of the operation of the second device.

  Hereinafter, the determination of the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex in accordance with the above-described concept is also referred to as “second control method”.

<Air-fuel ratio control>
The idea of air-fuel ratio control in the second device is that the upstream target air-fuel ratio abyfr is calculated only in accordance with the following equations (14) and (15) when both air-fuel ratio control and exhaust gas temperature control are performed. This is different from the idea of air-fuel ratio control in one device. In the following equations (14) and (15), DFex represents the exhaust gas temperature related change amount, Fbase represents the basic fuel injection amount, and abyfr (kref) represents the target air-fuel ratio at the reference time point kref.

DFexcon (k) = (DFex (k) + Fbase (k)) / Fbase (k) (14)
abyfr (k) = abyfr (kref) / DFexcon (k) (15)

  As understood from the above equation (14), the DFexcon calculated by the equation is “a value obtained by converting the exhaust gas temperature related variation amount DFex into a change rate with respect to the basic fuel injection amount Fbase”. Hereinafter, for convenience, this value is also referred to as “converted value DFexcon”. The conversion value DFexcon increases as the exhaust gas temperature related change amount DFex increases. Further, as understood from the above equation (15), the target air-fuel ratio abyfr calculated by the equation is smaller as the converted value DFexcon is larger (becomes a richer value).

  For example, when the exhaust gas temperature related variation amount DFex corresponds to 5% of the basic fuel injection amount Fbase, the conversion value DFexcon is 1.05. At this time, for example, if the target air-fuel ratio abyfr (kref) at the reference time point kref is the stoichiometric air-fuel ratio stoich, the target air-fuel ratio abyfr (k) calculated by the above equation (15) is stoich / 1.05.

  Here, if the intake air amount Ga at the reference time point kref and the time point k is the same, the basic fuel injection amount corresponding to the target air-fuel ratio stoich / 1.05 is 1.05 × Ga / stoich. This basic fuel injection amount 1.05 × Ga / stoich is equal to a value obtained by multiplying a basic fuel injection amount (Ga / stoich) corresponding to the original target air-fuel ratio stoich by a converted value 1.05. Thus, when the exhaust gas temperature related change amount DFex corresponds to 5% of the basic fuel injection amount Fbase, the basic fuel injection amount Fbase is increased by 5% (multiplied by 1.05).

That is, when the amount of fuel is increased by the exhaust gas temperature control, the basic fuel injection amount is increased by an amount corresponding to the exhaust gas temperature related change amount. Therefore, when air-fuel ratio control is performed in parallel with exhaust gas temperature control, the final fuel injection amount Fi is reliably increased by an amount necessary for exhaust gas temperature control (exhaust gas temperature related variation amount DFex). Thereby, the temperature of exhaust gas is appropriately reduced by the fuel cooling effect.
The above is the exhaust gas temperature control performed by the second device.

<Exhaust gas temperature control>
The concept of exhaust gas temperature control in the second device is the same as the concept of exhaust gas temperature control in the first device. Therefore, the description of the exhaust gas temperature control in the second device is omitted.

<Example of control by second control method>
The second device performs the above-described air-fuel ratio control and exhaust gas temperature control in accordance with the “second control method”. Hereinafter, an example in which air-fuel ratio control and exhaust gas temperature control (both or one) are performed will be described with reference to FIG. FIG. 12 is a time chart illustrating an example in which the second device “executes” control according to the second control method. In FIG. 12, a waveform in which the actual waveform of each value is schematically shown is shown for easy understanding. FIG. 12 is a time chart based on the premise that the air-fuel ratio related variation amount DFaf when the air-fuel ratio control is being performed is a positive value.

  Only air-fuel ratio control is performed at time ta in the time chart shown in FIG. At this time ta, as described above, the intake air amount Ga is the value Ga1, and the convergence temperature Tf and the current temperature Tp are both lower than the threshold temperature Tcatth. Further, at time ta, the target air-fuel ratio A / Ftgt is set to the stoichiometric air-fuel ratio stoich, and the air-fuel ratio related variation amount DFaf is the value a. Further, the exhaust gas temperature related variation amount DFex is zero. Therefore, the total DFaf + DFex is the value a. As a result, the actual air-fuel ratio A / F matches the target air-fuel ratio (theoretical air-fuel ratio stoich). As a result, the NOx emission amount is a value near zero.

  Thereafter, the intake air amount Ga increases from the value Ga1 to the value Ga2 at the time tb, and both the convergence temperature Tf and the current temperature Tp become equal to or higher than the threshold temperature Tcatth at the time tc. At this time, the air-fuel ratio control is “continued” and the exhaust gas temperature control is started.

  More specifically, first, the exhaust gas temperature related variation amount DFex changes from zero to the value b at time tc by exhaust gas temperature control. Further, the target air-fuel ratio A / Ftgt at time tc is calculated according to the above equations (14) and (15) in consideration of the exhaust gas temperature related variation amount DFex. More specifically, the converted value DFexcon of the exhaust gas temperature related variation amount DFex (value b) is calculated according to the above equation (14). Further, according to the above equation (15), the value obtained by dividing the target air-fuel ratio A / Ftgt (theoretical air-fuel ratio stoich) at the reference time point kref (in this example, time ta, time tb or time tc) by the converted value DFexcon is The target air-fuel ratio A / Ftgt at time tc is adopted.

  In this example, the exhaust gas temperature related variation amount DFex (value b) is a positive value, and the converted value DFexcon is a value larger than 1. Accordingly, the target air-fuel ratio A / Ftgt (stoich / DFexcon in FIG. 12) at time tc is a value (rich side value) smaller than the stoichiometric air-fuel ratio stoich.

  Then, the air-fuel ratio related change amount DFaf is determined so that the target air-fuel ratio A / Ftgt matches the actual air-fuel ratio A / F. Here, as described above, the target air-fuel ratio A / Ftgt is ensured that the final fuel injection amount Fi is the exhaust gas temperature-related change amount DFex even when the exhaust gas temperature control and the air-fuel ratio control are performed in parallel. This value is increased to Therefore, the air-fuel ratio related variation amount DFaf at time tc is the same value a as the value at the time before time tc.

  Therefore, the total DFaf + DFex (a + b) at time tc is larger than the value a. As a result, at the time tc, the actual air-fuel ratio A / F becomes a value (rich side value) smaller than the stoichiometric air-fuel ratio stoich.

  As a result, at time tc, the actual air-fuel ratio A / F also becomes an air-fuel ratio richer than the stoichiometric air-fuel ratio stoich. Therefore, a fuel cooling effect is appropriately obtained, and the temperature of the exhaust gas is appropriately reduced. Furthermore, as described above, even if the air-fuel ratio of the exhaust gas departs from the stoichiometric air-fuel ratio stoich toward the rich side, the NOx purification rate does not decrease to an unacceptable level. Therefore, at the time tc, the NOx emission amount is substantially maintained at a value near zero.

  Thereafter, as described above, the intake air amount Ga decreases from the value Ga2 to the value Ga1 at the time te, and both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth at the time tf. At this time, the exhaust gas temperature control is ended, and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is continued.

Thus, when the control according to the second control method of the present invention is performed, the temperature of the exhaust gas can be appropriately reduced even during the period in which the exhaust gas temperature control is performed. Furthermore, it is possible to prevent the NOx emission amount from increasing even during the same period.
The above is an example of control by the second control method.

<Actual operation>
Hereinafter, the actual operation of the second device will be described.
In the second device, the CPU 81 performs FIG. 13 for the control of fuel injection, FIG. 9 for the calculation of the exhaust gas temperature related change amount, FIG. 10 for the calculation of the main feedback amount, and FIG. 11 for the calculation of the sub feedback amount. The routines shown in (1) and (2) are repeatedly executed at predetermined timings.

  The second device is different from the first device only in that the CPU 81 executes the flowchart shown in FIG. 13 instead of the flowchart shown in FIG. Thus, hereinafter, each routine executed by the CPU 81 will be described focusing on this difference.

  The CPU 81 calculates the convergence temperature Tf (k) and the current temperature Tp (k) of the catalyst 53 by repeatedly executing the routine of FIG. 9 at predetermined timings as in the first device, and both of them are calculated. The exhaust gas temperature related variation amount DFex (k) is determined according to whether the temperature is equal to or higher than the threshold temperature Tcatth. Further, as in the first device, the CPU 81 repeatedly executes the routines of FIG. 10 and FIG. 11 at predetermined timings, so that the main feedback amount (air-fuel ratio related) is considered while taking the exhaust gas temperature related change amount DFex (k) into consideration. Change amount) DFaf (k) is determined.

  Further, the CPU 81 repeatedly executes the “second fuel injection control routine” shown by the flowchart in FIG. 13 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θf. In this routine, the CPU 81 determines the final fuel injection amount Fi in consideration of the air-fuel ratio related change amount DFaf and the exhaust gas temperature related change amount DFex, as well as the routine of FIG. Is injected from the injector 34.

  The routine shown in FIG. 13 is different from the routine shown in FIG. 8 only in that step 1310 and step 1310 are added. Therefore, steps for performing the same processing as the steps shown in FIG. 8 in FIG. 13 are denoted by the same reference numerals as those in FIG. Detailed description of these steps will be omitted as appropriate.

  Specifically, the CPU 81 starts processing from step 1300 in FIG. 13 at the above timing, proceeds to step 810, and determines the target air-fuel ratio abyfr (k) at the present time. Next, the CPU 81 proceeds to step 820 to determine whether or not the exhaust gas temperature related change amount DFex (k) at the present time is zero (that is, whether or not exhaust gas temperature control is being performed).

  When the exhaust gas temperature related change amount DFex (k) at the present time is zero (that is, when the exhaust gas temperature control is not “executed”), the CPU 81 determines “Yes” in step 820, and steps 830 to 830. The process of 880 is executed in the same manner as the first device. Thus, the basic fuel injection amount Fbase (k) determined based on the upstream target air-fuel ratio abyfr (k) is corrected by the main feedback amount DFaf (k) and the exhaust gas temperature related variation amount DFex (k), The fuel of the final fuel injection amount Fi (k) is injected into the fuel injection cylinder.

  On the other hand, when the exhaust gas temperature related variation amount DFex (k) at the current time is not zero (that is, when the exhaust gas temperature control is “executed”), the CPU 81 determines “No” in step 820. Proceed to step 1310. In step 1310, the CPU 81 calculates a converted value DFexcon (k) of the exhaust gas temperature related variation amount DFex (k) according to the above equation (14).

  Next, the CPU 81 proceeds to step 1320. In step 1320, the CPU 81 obtains a value obtained by dividing the target air-fuel ratio abyfr (kref) at the reference time point kref by the converted value DFexcon (k) according to the above equation (15), and uses the upstream target air-fuel ratio abyfr (k ) Is stored (updated).

  Thereafter, the CPU 81 executes the processing of step 830 to step 880 following step 1320 in the same manner as described above. Accordingly, the basic fuel injection amount Fbase (k) corresponding to the updated upstream target air-fuel ratio abyfr (k) is calculated (see step 840). The basic fuel injection amount Fbase (k) is corrected by the main feedback amount DFaf (k) and the exhaust gas temperature related change amount DFex (k), and the fuel of the final fuel injection amount Fi (k) is supplied to the fuel injection cylinder. Supplied.

  As described above, when the exhaust gas temperature control is performed (when the exhaust gas temperature related change amount DFex is not zero), the second device calculates the upstream target air-fuel ratio abyfr based on the exhaust gas temperature related change amount DFex. to correct. As a result, even when exhaust gas temperature control and air-fuel ratio control are performed in parallel, the final fuel injection amount Fi is reliably changed (increased) by an amount necessary for exhaust gas temperature control (exhaust gas temperature related change amount DFex). ) As a result, the temperature of the exhaust gas is appropriately reduced, and the NOx emission amount is substantially maintained at a value near zero.

As can be understood from the above description, the second device follows the above routines regardless of whether the air-fuel ratio related variation amount DFaf (kref) at the reference time point kref is a positive value or a negative value. An appropriate air-fuel ratio related change amount DFaf and exhaust gas temperature related change amount DFex can be determined.
The above is the description of the second embodiment of the present invention.

(Third embodiment)
Next, a control device according to a third embodiment of the present invention (hereinafter also referred to as “third device”) will be described.

<Outline of device>
The third device is applied to an engine having a configuration similar to that of the engine 10 to which the first device is applied (see FIG. 1, hereinafter referred to as “the engine 10” for convenience). Therefore, the description of the outline of the device to which the third device is applied is omitted.

<Outline of device operation>
When the exhaust gas temperature control is performed, the third device is different from the first device in that “the exhaust gas temperature related change amount DFex is corrected” and “the air-fuel ratio control is not performed” as necessary.

  More specifically, when the exhaust gas temperature related change amount DFex (k) is determined, the third device determines that the exhaust gas temperature related change amount DFex (k) is the air-fuel ratio related change amount DFaf (kref) at the reference time point kref. If smaller, the exhaust gas temperature related variation amount DFex is corrected to “a value greater than or equal to the air / fuel ratio related variation amount DFaf (kref)”.

The third device performs the exhaust gas temperature control using the exhaust gas temperature related change amount DFex (k) corrected as described above, and “stops” the air-fuel ratio control.
The above is the outline of the operation of the third device.

  Hereinafter, the determination of the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex in accordance with the above-described concept is also referred to as a “third control method”.

<Air-fuel ratio control>
The idea of the air / fuel ratio control in the third device is that the main feedback amount DFaf is set to zero when the exhaust gas temperature control is performed (that is, the air / fuel ratio control is not performed). It is different from the idea. Therefore, a detailed description of the air-fuel ratio control in the third device is omitted.

<Exhaust gas temperature control>
First, the third device calculates the exhaust gas temperature related change amount DFex at the present time (time k) according to the same concept as the first device. When the exhaust gas temperature related change amount DFex (k) calculated in this way is smaller than the air-fuel ratio related change amount DFaf (kref) at the reference time point kref, the third device sets the exhaust gas temperature related change amount DFex (k) to “ It is changed (updated) to a value DFexlarge which is not less than the air-fuel ratio related change amount DFaf (kref).

Then, the third device corrects the basic fuel injection amount Fbase using the changed (updated) exhaust gas temperature related change amount DFex (that is, DFexlarge) according to the equation (12).
The above is the exhaust gas temperature control performed by the third device.

<Example of control by third control method>
The third device performs the above-described air-fuel ratio control and exhaust gas temperature control in accordance with the “third control method”. Hereinafter, an example in which air-fuel ratio control and exhaust gas temperature control (both or one) are performed will be described with reference to FIG. FIG. 14 is a time chart illustrating an example in which the third device “executes” control according to the third control method. In FIG. 14, a waveform in which the actual waveform of each value is schematically shown is shown for easy understanding. FIG. 14 is a time chart on the assumption that the air-fuel ratio related variation amount DFaf when the air-fuel ratio control is being performed is a positive value.

  Only air-fuel ratio control is performed at time ta in the time chart shown in FIG. At this time ta, as described above, the intake air amount Ga is the value Ga1, and the convergence temperature Tf and the current temperature Tp are both lower than the threshold temperature Tcatth. Further, at time ta, the target air-fuel ratio A / Ftgt is set to the stoichiometric air-fuel ratio stoich, and the air-fuel ratio related variation amount DFaf is the value a. Further, the exhaust gas temperature related variation amount DFex is zero. Therefore, the total DFaf + DFex is the value a. As a result, the actual air-fuel ratio A / F matches the target air-fuel ratio (theoretical air-fuel ratio stoich). As a result, the NOx emission amount is a value near zero.

  Thereafter, the intake air amount Ga increases from the value Ga1 to the value Ga2 at the time tb, and both the convergence temperature Tf and the current temperature Tp become equal to or higher than the threshold temperature Tcatth at the time tc. At this time, the air-fuel ratio control is “stopped” and the exhaust gas temperature control is started.

  More specifically, the air-fuel ratio related change amount DFaf decreases from the value a to zero at time tc by stopping the air-fuel ratio control. Further, the exhaust gas temperature related change amount DFex (in this example, the value b) is determined by the exhaust gas temperature related change amount table MapDFex (NE, Ga). At this time, it is assumed that the exhaust gas temperature related change amount DFex (value b) is smaller than the air-fuel ratio related change amount DFaf (value a) at the reference time point kref (in this example, time ta, time tb or time tc). According to this assumption, as described above, the exhaust gas temperature related change amount DFex (value b) at the time tc is equal to or greater than the air-fuel ratio related change amount DFaf (value a) at the reference time point kref (in this example, the value d) is corrected.

  Therefore, the total DFaf + DFex (value d) at time tc is larger than value a. As a result, at the time tc, the actual air-fuel ratio A / F becomes a value (rich side value) smaller than the stoichiometric air-fuel ratio stoich. Note that since the air-fuel ratio control is stopped at time tc, the target air-fuel ratio A / Ftgt is not set (see the broken line in the figure).

  As a result, at time tc, the air-fuel ratio of the catalyst introduction gas also becomes richer than the stoichiometric air-fuel ratio stoich. Therefore, a fuel cooling effect is appropriately obtained, and the temperature of the exhaust gas is appropriately reduced. Furthermore, as described above, even if the air-fuel ratio of the exhaust gas departs from the stoichiometric air-fuel ratio stoich toward the rich side, the NOx purification rate does not decrease to an unacceptable level. Therefore, at the time tc, the NOx emission amount is substantially maintained at a value near zero.

  Thereafter, as described above, the intake air amount Ga decreases from the value Ga2 to the value Ga1 at the time te, and both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth at the time tf. At this time, the exhaust gas temperature control is ended, and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is resumed.

Thus, when the control according to the third control method of the present invention is performed, the temperature of the exhaust gas can be appropriately reduced even during the period in which the exhaust gas temperature control is performed. Furthermore, it is possible to prevent the NOx emission amount from increasing even during the same period.
The above is an example of control by the third control method.

<Actual operation>
Hereinafter, the actual operation of the third device will be described.
In the third device, the CPU 81 performs FIG. 8 for the control of fuel injection, FIG. 15 for the calculation of the exhaust gas temperature related change amount, FIG. 16 for the calculation of the main feedback amount, and FIG. 11 for the calculation of the sub feedback amount. The routines shown in (1) and (2) are repeatedly executed at predetermined timings.

  The third device is different from the first device only in that the CPU 81 executes the flowcharts shown in FIG. 15 and FIG. 16 instead of the flowcharts shown in FIGS. 9 and 10. Thus, hereinafter, each routine executed by the CPU 81 will be described focusing on this difference.

  The CPU 81 repeatedly executes the “third exhaust gas temperature related change amount calculation routine” shown by the flowchart in FIG. 15 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θf. The CPU 81 calculates the exhaust gas temperature related change amount DFex by this routine.

  The routine shown in FIG. 15 differs from the routine shown in FIG. 9 only in that step 1510 and step 1520 are added. Accordingly, steps for performing the same processing as the steps shown in FIG. 9 in FIG. 15 are denoted by the same reference numerals as those given to such steps in FIG. Detailed description of these steps will be omitted as appropriate.

  Specifically, when the CPU 81 starts processing from step 1500 in FIG. 15 at the above timing, the process proceeds to step 930 via step 910 and step 920. If both the convergence temperature Tf (k) and the current temperature Tp (k) are equal to or higher than the threshold temperature Tcatth, the CPU 81 proceeds to step 950 and calculates the exhaust gas temperature related change amount DFex (k).

  Next, the CPU 81 proceeds to step 1510. In step 1510, the CPU 81 determines whether or not the exhaust gas temperature related change amount DFex (k) at the current time is smaller than the main feedback amount DFaf (kref) at the reference time kref. As described above, the CPU 81 stores the time (time k) when the determination result in step 930 changes from “No” to “Yes” as the reference time kref in the RAM 83.

  When the exhaust gas temperature related change amount DFex (k) at the present time is the main feedback amount DFaf (kref) “more than” at the reference time point kref, the CPU 81 makes a “No” determination at step 1510, and proceeds to step 1595. The routine is temporarily terminated. Therefore, in this case, the basic fuel injection amount Fbase (k) is corrected using the exhaust gas temperature related variation amount DFex (k) calculated in step 950 (see step 850 in FIG. 8).

  On the other hand, if the exhaust gas temperature related change amount DFex (k) at the current time is “smaller” than the main feedback amount DFaf (kref) at the reference time kref, the CPU 81 determines “Yes” in step 1510, and step 1520. Proceed to In step 1520, the CPU 81 stores “a change amount DFexlarge greater than or equal to the air-fuel ratio related change amount DFaf (kref) at the reference time point kref” in the exhaust gas temperature related change amount DFex (k). Thereafter, the CPU 81 proceeds to step 1595 to end the present routine tentatively. Therefore, in this case, the exhaust gas temperature related change amount DFex (k) is changed to the change amount DFexlarge, and the basic fuel injection amount Fbase is corrected using the change amount DFexlarge (see step 850 in FIG. 8). .

  Further, the CPU 81 repeatedly executes the “third air-fuel ratio related change amount (main feedback amount) calculation routine” shown by the flowchart in FIG. 16 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θg. . The CPU 81 calculates the main feedback amount DFaf by this routine.

  The routine shown in FIG. 16 differs from the routine shown in FIG. 10 only in that step 1050 is “deleted”. Therefore, in FIG. 16, steps for performing the same processing as the steps shown in FIG. 10 are denoted by the same reference numerals as those given to such steps in FIG. 10. Detailed description of these steps will be omitted as appropriate.

  Specifically, when the CPU 81 starts processing from step 1600 in FIG. 16 at the above timing, if the main feedback control condition is satisfied, the process proceeds to step 1010 via step 1005. When the exhaust gas temperature related change amount DFex (k) at the present time is zero (that is, when the exhaust gas temperature control is not performed), the CPU 81 determines “Yes” in step 1010, and performs steps 1010 to 1045. Then, the process proceeds to step 1695 to end the present routine tentatively. Thereby, the main feedback amount DFaf (k) is determined.

  On the other hand, when the exhaust gas temperature related change amount DFex (k) at the current time is not zero (that is, when the exhaust gas temperature control is performed), the CPU 81 makes a “No” determination at step 1010, and steps 1055 and 1060. Then, the process proceeds to step 1695 to end the present routine tentatively. Thereby, zero is set as the main feedback amount DFaf (k).

  Thus, when exhaust gas temperature control is performed (when it is determined as “No” in Step 1010), zero is always set as the main feedback amount DFaf (k). That is, the air-fuel ratio control is “stopped”.

  As described above, the third device stops the air-fuel ratio control when the exhaust gas temperature control is being performed (when the exhaust gas temperature related change amount DFex is not zero). Further, the third device corrects the exhaust gas temperature related variation amount DFex to “an amount greater than the air / fuel ratio related variation amount DFaf at the reference time point kref” as necessary. As a result, even if the air-fuel ratio control is stopped when the exhaust gas temperature control is performed, the final fuel injection amount Fi is reliably changed (increased). As a result, the temperature of the exhaust gas is appropriately reduced, and the NOx emission amount is substantially maintained at a value near zero.

As can be understood from the above description, the third device follows the above routines regardless of whether the air-fuel ratio related change amount DFaf (kref) at the reference time point kref is a positive value or a negative value. An appropriate exhaust gas temperature related change amount DFex can be determined.
The above is the description of the third embodiment of the present invention.

(Fourth embodiment)
Next, a control device according to a fourth embodiment of the present invention (hereinafter also referred to as “fourth device”) will be described.

<Outline of device>
The fourth device is applied to an engine having the same configuration as the engine 10 to which the first device is applied (see FIG. 1, hereinafter referred to as “engine 10” for convenience). Therefore, the description of the outline of the device to which the fourth device is applied is omitted.

<Outline of device operation>
When the exhaust gas temperature control is performed, the fourth device is different from the first device in that “the exhaust gas temperature related change amount DFex is corrected” and “the air-fuel ratio control is not performed” as necessary. Furthermore, the fourth device is different from the third device in that “the exhaust gas temperature related change amount DFex is corrected by a different concept from the third device”.

  More specifically, when the exhaust gas temperature related change amount DFex (k) is determined, the fourth device determines that the exhaust gas temperature related change amount DFex (k) is the air-fuel ratio related change amount DFaf (kref) at the reference time point kref. Is smaller than that, the exhaust gas temperature related variation amount DFex is corrected to “the sum of the exhaust gas temperature related variation amount DFex and the air-fuel ratio related variation amount DFaf (kref)”.

The fourth device performs the exhaust gas temperature control using the modified exhaust gas temperature related variation amount DFex (k), and “stops” the air-fuel ratio control.
The above is the outline of the operation of the fourth device.

  Hereinafter, the determination of the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex according to the above-described concept is also referred to as a “fourth control method”.

<Air-fuel ratio control>
The idea of the air / fuel ratio control in the fourth device is that the main feedback amount DFaf is set to zero when the exhaust gas temperature control is performed (that is, the air / fuel ratio control is not performed). It is different from the idea. Therefore, detailed description of the air-fuel ratio control in the fourth device is omitted.

<Exhaust gas temperature control>
First, the fourth device calculates the exhaust gas temperature related change amount DFex at the present time (time k) according to the same concept as the first device. When the exhaust gas temperature related change amount DFex (k) calculated in this way is smaller than the air-fuel ratio related change amount DFaf (kref) at the reference time point kref, the fourth device sets the exhaust gas temperature related change amount DFex (k) to “ Change (update) to “the sum of the exhaust gas temperature related change amount DFex (k) and the air-fuel ratio related change amount DFaf (kref)”.

Then, the fourth device corrects the basic fuel injection amount Fbase using the changed (updated) exhaust gas temperature related change amount DFex (that is, DFexlarge) according to the equation (12).
The above is the exhaust gas temperature control performed by the fourth device.

<Example of control by the fourth control method>
The fourth device performs the above-described air-fuel ratio control and exhaust gas temperature control in accordance with the “fourth control method”. Hereinafter, an example in which air-fuel ratio control and exhaust gas temperature control (both or one) are performed will be described with reference to FIG. FIG. 17 is a time chart illustrating an example in which the fourth device “executes” control according to the fourth control method. In FIG. 17, a waveform in which the actual waveform of each value is schematically shown is shown for easy understanding. FIG. 17 is a time chart on the assumption that the air-fuel ratio related variation amount DFaf when the air-fuel ratio control is being performed is a positive value.

  Only air-fuel ratio control is performed at time ta in the time chart shown in FIG. At this time ta, as described above, the intake air amount Ga is the value Ga1, and the convergence temperature Tf and the current temperature Tp are both lower than the threshold temperature Tcatth. Further, at time ta, the target air-fuel ratio A / Ftgt is set to the stoichiometric air-fuel ratio stoich, and the air-fuel ratio related variation amount DFaf is the value a. Further, the exhaust gas temperature related variation amount DFex is zero. Therefore, the total DFaf + DFex is the value a. As a result, the actual air-fuel ratio A / F matches the target air-fuel ratio (theoretical air-fuel ratio stoich). As a result, the NOx emission amount is a value near zero.

  Thereafter, the intake air amount Ga increases from the value Ga1 to the value Ga2 at the time tb, and both the convergence temperature Tf and the current temperature Tp become equal to or higher than the threshold temperature Tcatth at the time tc. At this time, the air-fuel ratio control is “stopped” and the exhaust gas temperature control is started.

  More specifically, the air-fuel ratio related change amount DFaf decreases from the value a to zero at time tc by stopping the air-fuel ratio control. Further, the exhaust gas temperature related change amount DFex (in this example, the value b) is determined by the exhaust gas temperature related change amount table MapDFex (NE, Ga). At this time, it is assumed that the exhaust gas temperature related change amount DFex (value b) is smaller than the air-fuel ratio related change amount DFaf (value a) at the reference time point kref (in this example, time ta, time tb or time tc). According to this assumption, as described above, the exhaust gas temperature related change amount DFex (value b) at time tc is the exhaust gas temperature related change amount DFex (value b) and the air-fuel ratio related change amount DFaf (value b) at the reference time point kref. a) and the sum (in this example, value a + b).

  Therefore, the total DFaf + DFex (value a + b) at time tc is larger than value a. As a result, at the time tc, the actual air-fuel ratio A / F becomes a value (rich side value) smaller than the stoichiometric air-fuel ratio stoich. Note that since the air-fuel ratio control is stopped at time tc, the target air-fuel ratio A / Ftgt is not set (see the broken line in the figure).

  As a result, at time tc, the air-fuel ratio of the catalyst introduction gas also becomes richer than the stoichiometric air-fuel ratio stoich. Therefore, a fuel cooling effect is appropriately obtained, and the temperature of the exhaust gas is appropriately reduced. Furthermore, as described above, even if the air-fuel ratio of the exhaust gas departs from the stoichiometric air-fuel ratio stoich toward the rich side, the NOx purification rate does not decrease to an unacceptable level. Therefore, at the time tc, the NOx emission amount is substantially maintained at a value near zero.

  Thereafter, as described above, the intake air amount Ga decreases from the value Ga2 to the value Ga1 at the time te, and both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth at the time tf. At this time, the exhaust gas temperature control is ended, and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is resumed.

Thus, when the control according to the fourth control method of the present invention is performed, the temperature of the exhaust gas can be appropriately reduced even during the period in which the exhaust gas temperature control is performed. Furthermore, it is possible to prevent the NOx emission amount from increasing even during the same period.
The above is an example of control by the fourth control method.

<Actual operation>
Hereinafter, the actual operation of the fourth device will be described.
In the fourth device, the CPU 81 performs FIG. 8 regarding the control of fuel injection, FIG. 18 regarding the calculation of the exhaust gas temperature related change amount, FIG. 16 regarding the calculation of the main feedback amount, and FIG. 11 regarding the calculation of the sub feedback amount. The routines shown in (1) and (2) are repeatedly executed at predetermined timings.

  The fourth device is different from the first device only in that the CPU 81 executes the flowcharts shown in FIG. 18 and FIG. 16 instead of the flowcharts shown in FIGS. 9 and 10. Thus, hereinafter, each routine executed by the CPU 81 will be described focusing on this difference. Note that FIG. 16 has already been described as the main feedback amount calculation routine in the third device.

  The CPU 81 repeatedly executes the “fourth exhaust gas temperature related change amount calculation routine” shown by the flowchart in FIG. 18 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θf. The CPU 81 calculates the exhaust gas temperature related change amount DFex by this routine.

  The routine shown in FIG. 18 differs from the routine shown in FIG. 9 only in that step 1810 and step 1820 are added. Therefore, steps for performing the same processing as the steps shown in FIG. 9 in FIG. 18 are denoted by the same reference numerals as those given to such steps in FIG. Detailed description of these steps will be omitted as appropriate.

  Specifically, when the CPU 81 starts processing from step 1800 in FIG. 18 at the above timing, the process proceeds to step 930 via step 910 and step 920. If both the convergence temperature Tf (k) and the current temperature Tp (k) are equal to or higher than the threshold temperature Tcatth, the CPU 81 proceeds to step 950 and calculates the exhaust gas temperature related change amount DFex (k).

  Next, the CPU 81 proceeds to step 1810. In step 1810, the CPU 81 determines whether or not the exhaust gas temperature related change amount DFex (k) at the current time is smaller than the main feedback amount DFaf (kref) at the reference time kref. As described above, the CPU 81 stores the time (time k) when the determination result in step 930 changes from “No” to “Yes” as the reference time kref in the RAM 83.

  When the exhaust gas temperature related change amount DFex (k) at the present time is the main feedback amount DFaf (kref) “more than” at the reference time point kref, the CPU 81 makes a “No” determination at step 1810 and proceeds to step 1895 to proceed to this step. The routine is temporarily terminated. Therefore, in this case, the basic fuel injection amount Fbase (k) is corrected using the exhaust gas temperature related variation amount DFex (k) calculated in step 950 (see step 850 in FIG. 8).

  On the other hand, if the exhaust gas temperature related change amount DFex (k) at the current time is “smaller” than the main feedback amount DFaf (kref) at the reference time kref, the CPU 81 determines “Yes” in step 1810, and step 1820. Proceed to In step 1820, the CPU 81 stores “the sum of the exhaust gas temperature related change amount DFex (k) and the air / fuel ratio related change amount DFaf (kref) at the reference time point kref” in the exhaust gas temperature related change amount DFex (k). To do. Thereafter, the CPU 81 proceeds to step 1895 to end the present routine tentatively. Therefore, in this case, the exhaust gas temperature related change amount DFex (k) is changed to the “sum”, and the basic fuel injection amount Fbase is corrected using the “sum” (see step 850 in FIG. 8). ).

  As described above, the fourth device stops the air-fuel ratio control when the exhaust gas temperature control is performed, and sets the exhaust gas temperature related change amount DFex as “the exhaust gas temperature related change amount DFex and the reference time point kref as necessary. To the sum of the air-fuel ratio related change amount DFaf in As a result, even if the air-fuel ratio control is stopped when the exhaust gas temperature control is performed, the final fuel injection amount Fi is reliably changed (increased). For this reason, the temperature of the exhaust gas is appropriately lowered, and the NOx emission amount is maintained at a value in the vicinity of substantially zero.

As can be understood from the above description, the fourth device follows the above routines regardless of whether the air-fuel ratio related change amount DFaf (kref) at the reference time point kref is a positive value or a negative value. An appropriate exhaust gas temperature related change amount DFex can be determined.
The above is the description of the fourth embodiment of the present invention.

(Fifth embodiment)
Next, a control device according to a fifth embodiment of the present invention (hereinafter also referred to as “fifth device”) will be described.

<Outline of device>
The fifth device is applied to an engine having the same configuration as the engine 10 to which the first device is applied (see FIG. 1, hereinafter referred to as “engine 10” for convenience). Therefore, the description of the outline of the device to which the fifth device is applied is omitted.

<Outline of device operation>
The fifth device is different from the first device in that the exhaust gas temperature related change amount DFex is changed according to the temperature of the catalyst 53 when the exhaust gas temperature control is performed.

  More specifically, when the exhaust gas temperature control is performed, the fifth device determines that the exhaust gas temperature related change amount DFex is “a reference change amount DFexbase determined based on the operating state of the engine 10 and the temperature of the catalyst 53 is taken into consideration. An amount obtained by multiplying a predetermined correction coefficient CRex (correction change amount) ”is employed.

  Further, like the first device, the fifth device “continues” the air-fuel ratio control even when the exhaust gas temperature control is performed. At this time, the fifth device employs “the air-fuel ratio determined in consideration of the exhaust gas temperature related variation amount DFex” as in the second device, as the upstream target air-fuel ratio abyfr (k) in the air-fuel ratio control.

The fifth device performs exhaust gas temperature control using the exhaust gas temperature related variation amount DFex (k) determined as described above, and performs air-fuel ratio control according to the upstream target air-fuel ratio abyfr (k) determined as described above. I do.
The above is the outline of the operation of the fifth device.

  Hereinafter, determining the air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex in accordance with the above-described concept is also referred to as “fifth control method”.

<Air-fuel ratio control>
The idea of air-fuel ratio control in the fifth device is the same as the idea of air-fuel ratio control in the second device (not the first device). Therefore, detailed description of the air-fuel ratio control in the fifth device is omitted.

<Exhaust gas temperature control>
First, the fifth device calculates a reference change amount DFexbase based on the operating state of the engine 10. More specifically, the fifth device has a current reference change amount table MapDFexbase (NE, Ga) that defines the “relationship between the engine speed NE, the intake air amount Ga, and the reference change amount DFexbase”. By applying the engine speed NE (k) and the intake air amount Ga (k), the current reference change amount DFexbase (k) is calculated. This reference change amount DFexbase is determined as an appropriate value larger than the air-fuel ratio related change amount DFaf (kref) at the reference time point kref.

  Next, the fifth device calculates a correction coefficient CRex for correcting the reference change amount DFexbase according to the following equations (16) and (17). In the following equation (16), Tcatth represents the threshold temperature Tcatth of the catalyst 53.

If Tp <Tf:
CRex (k) = {Tp (k) −Tcatth} / {Tf (k) −Tcatth} (16)
When Tp ≧ Tf:
CRex (k) = 1 (17)

  Next, the fifth device calculates the exhaust gas temperature related variation amount DFex (k) according to the following equation (18).

      DFex (k) = DFexbase (k) × CRex (k) (18)

  As can be understood from the above equation (16), the correction coefficient CRex calculated by the equation is a value of 1 or less and approaches 1 as the current temperature Tp approaches the convergence temperature Tf. Therefore, the exhaust gas temperature related change amount DFex obtained by multiplying the reference change amount DFexbase by the correction coefficient CRex increases as the current temperature Tp approaches the convergence temperature Tf. As a result, the exhaust gas temperature related change amount DFex increases as the current temperature Tp approaches the convergence temperature Tf (that is, the current temperature Tp increases toward the convergence temperature Tf). Will be reduced.)

Further, as understood from the above equation (17), when the current temperature Tp is equal to or higher than the convergence temperature Tf (that is, when the current temperature Tp decreases toward the convergence temperature Tf), the correction coefficient CRex is maintained at 1. Is done. Thereby, in this case, the exhaust gas temperature related change amount DFex is maintained at the reference change amount DFexbase.
The above is the exhaust gas temperature control performed by the fifth device.

<Example of control by fifth control method>
The fifth device performs the above-described air-fuel ratio control and exhaust gas temperature control in accordance with the “fifth control method”. Hereinafter, an example in which air-fuel ratio control and exhaust gas temperature control (both or one) are performed will be described with reference to FIG. FIG. 19 is a time chart illustrating an example in which the fifth device “executes” control according to the fifth control method. In FIG. 19, a waveform in which the actual waveform of each value is schematically shown is shown for easy understanding. FIG. 19 is a time chart on the assumption that the air-fuel ratio related change amount DFaf is a positive value when the air-fuel ratio control is being performed.

  Only air-fuel ratio control is performed at time ta in the time chart shown in FIG. At this time ta, as described above, the intake air amount Ga is the value Ga1, and the convergence temperature Tf and the current temperature Tp are both lower than the threshold temperature Tcatth. Further, at time ta, the target air-fuel ratio A / Ftgt is set to the stoichiometric air-fuel ratio stoich, and the air-fuel ratio related variation amount DFaf is the value a. Further, the exhaust gas temperature related variation amount DFex is zero. Therefore, the total DFaf + DFex is the value a. As a result, the actual air-fuel ratio A / F matches the target air-fuel ratio (theoretical air-fuel ratio stoich). As a result, the NOx emission amount is a value near zero.

  Thereafter, the intake air amount Ga increases from the value Ga1 to the value Ga2 at the time tb, and both the convergence temperature Tf and the current temperature Tp become equal to or higher than the threshold temperature Tcatth at the time tc. At this time, the air-fuel ratio control is “continued” and the exhaust gas temperature control is started.

  Specifically, first, a reference change amount DFexbase (in this example, a value e) is determined at time tc in relation to exhaust gas temperature control. Here, since the current temperature Tp at time tc is lower than the convergence temperature Tf, the correction coefficient CRex is determined according to the above equation (16). Then, the exhaust gas temperature related change amount DFex is calculated by multiplying the reference change amount DFexbase by the correction coefficient CRex. Specifically, since the current temperature Tp at time tc matches the threshold temperature Tcatth, the correction coefficient CRex is zero. Therefore, the exhaust gas temperature related variation amount DFex at time tc is zero.

  Thereafter, as the time elapses, the current temperature Tp increases toward the convergence temperature Tf, so that the correction coefficient CRex increases toward 1. Therefore, the exhaust gas temperature related variation amount DFex increases with time. As described above, during the period in which the exhaust gas temperature related change amount DFex increases (from time tc to time tg to be described later), the air-fuel ratio related change amount DFaf is determined at time tc as in the above-mentioned example of control by the second control method. It is maintained at the value (value a) at an earlier time point. Therefore, after time tc, the total DFaf + DFex gradually increases from the value a, and the actual air-fuel ratio A / F gradually decreases from the stoichiometric air-fuel ratio stoich (becomes a rich value).

  As a result, in the period from time tc to time tg described later, the temperature of the exhaust gas is appropriately reduced, and the NOx emission amount is substantially maintained at a value near zero.

  Thereafter, at time tg, the exhaust gas temperature related change amount DFex reaches the air-fuel ratio related change amount DFaf (value a) at the reference time point kref (in this example, time ta, time tb, or time tc). At this time, as described in the above “second control method”, the air-fuel ratio control is “stopped”. Therefore, at time tg, the air-fuel ratio related variation amount DFaf decreases from the value a to zero. Therefore, at time tg, the total DFaf + DFex decreases to the value a (corresponding to the exhaust gas temperature related variation amount DFex), and the actual air-fuel ratio A / F increases to the stoichiometric air-fuel ratio stoich.

  Thereafter, as time passes, the exhaust gas temperature related variation amount DFex increases as described above. Therefore, in the period from time tg to time tf described later, the total DFaf + DFex gradually increases from the value a, and the actual air-fuel ratio A / F gradually decreases from the stoichiometric air-fuel ratio stoich.

  As a result, even during the period from time tg to time tf, which will be described later, the temperature of the exhaust gas can be appropriately reduced, and the NOx emission amount is substantially maintained at a value near zero.

Thereafter, as described above, the intake air amount Ga decreases from the value Ga2 to the value Ga1 at the time te, and both the convergence temperature Tf and the current temperature Tp become lower than the threshold temperature Tcatth at the time tf. At this time, the exhaust gas temperature control is ended, and the air-fuel ratio control (the target air-fuel ratio A / Ftgt is the stoichiometric air-fuel ratio stoich) is resumed.
The above is an example of control by the fifth control method.

<Actual operation>
Hereinafter, the actual operation of the fifth device will be described.
In the fifth device, the CPU 81 performs FIG. 13 for control of fuel injection, FIG. 20 for calculation of the exhaust gas temperature related change amount, FIG. 10 for calculation of the main feedback amount, and FIG. 11 for calculation of the sub feedback amount. The routines shown in (1) and (2) are repeatedly executed at predetermined timings.

  The fifth device is different from the first device only in that the CPU 81 executes the flowchart shown in FIG. 20 instead of the flowchart shown in FIG. Thus, hereinafter, each routine executed by the CPU 81 will be described focusing on this difference. Note that FIG. 13 has already been described as the fuel injection control routine in the second device.

  The CPU 81 repeatedly executes the “fifth exhaust gas temperature related change amount calculation routine” shown by the flowchart in FIG. 20 at each timing when the crank angle of the fuel injection cylinder coincides with the crank angle θf. The CPU 81 calculates the reference change amount DFexbase of the exhaust gas temperature related change amount by this routine, and calculates the exhaust gas temperature related change amount DFex by multiplying the reference change amount DFexbase by the correction coefficient CRex.

  The routine shown in FIG. 20 differs from the routine shown in FIG. 9 in that step 950 is deleted and steps 2010 to 2050 are added. Therefore, steps for performing the same processing as the steps shown in FIG. 9 in FIG. 20 are denoted by the same reference numerals as those given to such steps in FIG. Detailed description of these steps will be omitted as appropriate.

  Specifically, when the CPU 81 starts processing from step 2000 in FIG. 20 at the above timing, the process proceeds to step 930 via step 910 and step 920. If both the convergence temperature Tf (k) and the current temperature Tp (k) are equal to or higher than the threshold temperature Tcatth, the CPU 81 determines “Yes” in step 930 and proceeds to step 2010.

  In step 2010, the CPU 81 applies the current engine speed NE (k) and the intake air amount Ga (k) to the reference change amount table MapDFexbase (NE, Ga) described above to thereby change the current reference change amount DFexbase. (K) is calculated.

  Next, the CPU 81 proceeds to step 2020. In step 2020, the CPU 81 determines whether or not the current temperature Tp (k) is lower than the convergence temperature Tf (k). If the current temperature Tp (k) is lower than the convergence temperature Tf (k), the CPU 81 determines “Yes” in step 2020 and proceeds to step 2030.

  In step 2030, the CPU 81 calculates the correction coefficient CRex (k) based on the current temperature Tp (k), the convergence temperature Tf (k), and the threshold temperature Tcatth according to the above equation (16).

  Next, the CPU 81 proceeds to step 2040. In step 2040, the CPU 81 calculates the exhaust gas temperature related change amount DFex (k) by multiplying the reference change amount DFexbase (k) by the correction coefficient CRex (k) according to the above equation (18). Thereafter, the CPU 81 proceeds to step 2095 to end the present routine tentatively.

  On the other hand, if the current temperature Tp (k) at the current time is equal to or higher than the convergence temperature Tf (k), the CPU 81 makes a “No” determination at step 2020 and proceeds to step 2050. In step 2050, the CPU 81 stores “1” in the correction coefficient CRex (k).

  Thereafter, the CPU 81 proceeds to step 2040 as described above, and calculates the exhaust gas temperature related change amount DFex (k). In this case, since the correction coefficient CRex (k) is 1, the exhaust gas temperature related change amount DFex (k) is the same as the reference change amount DFexbase (k). That is, in this case, the reference change amount DFexbase (k) is not corrected.

  Further, as in the second device, the CPU 81 repeatedly executes the routine of FIG. 13 at every predetermined timing. As a result, the upstream target air-fuel ratio abyfr (k) is corrected in accordance with the exhaust gas temperature related variation amount DFex (k) calculated as described above (see step 1310 and step 1320 in FIG. 13). The basic fuel injection amount Fbase (k) is corrected by the main feedback amount DFaf (k) determined based on the corrected upstream target air-fuel ratio abyfr (k) and the exhaust gas temperature related variation amount DFex (k). Then, the final fuel injection amount Fi (k) is calculated (see step 850 in FIG. 13).

  As described above, the fifth device changes the exhaust gas temperature related change amount DFex in accordance with the temperature of the catalyst 53. As a result, the temperature of the exhaust gas is appropriately reduced. Further, the fifth device corrects the upstream target air-fuel ratio abyfr based on the exhaust gas temperature related variation amount DFex. As a result, even when the exhaust gas temperature control and the air-fuel ratio control are performed in parallel, the final fuel injection amount Fi is reliably changed (increased) by the exhaust gas temperature related change amount DFex. As a result, the temperature of the exhaust gas is appropriately reduced, and the NOx emission amount is substantially maintained at a value near zero.

  In the fifth device, the concept of the exhaust gas temperature control (see the routine of FIG. 20) described above is applied to the control method shown in the second device. However, the concept of the exhaust gas temperature control of the fifth device may be applied to any of the first device and the third device to the fourth device.

As can be understood from the above description, the fifth device follows the above routines regardless of whether the air-fuel ratio related variation amount DFaf (kref) at the reference time point kref is a positive value or a negative value. An appropriate air-fuel ratio related change amount DFaf and exhaust gas temperature related change amount DFex can be determined.
The above is the description of the fifth embodiment of the present invention.

  By the way, the control devices (first device to fifth device) according to each of the above embodiments perform exhaust gas temperature control when “both” of the convergence temperature Tf and the current temperature Tp of the catalyst 53 are equal to or higher than the threshold temperature Tcatth. (For example, see step 930 in FIG. 9). However, the control device of the present invention can be configured to perform exhaust gas temperature control when “at least one” of the convergence temperature Tf and the current temperature Tp is equal to or higher than the threshold temperature Tcatth. That is, the control device of the present invention can be configured to perform exhaust gas temperature control when it is determined that the temperature of the catalyst may become excessively high.

<Summary of Embodiment>
As described above, the control device (first device to fifth device) according to each embodiment of the present invention is applied to the internal combustion engine 10 including the catalyst 53.

The first device of the present invention is
Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10, and the internal combustion engine 10 according to a first change amount DFaf determined so as to match the air-fuel ratio with the target air-fuel ratio abyfr. Air-fuel ratio control means (step 850 in FIG. 8, routine in FIGS. 10 and 11) for changing the amount of fuel supplied to
Exhaust gas temperature control means for controlling the temperature of the exhaust gas, the exhaust gas temperature control changing the amount of fuel supplied to the internal combustion engine 10 in accordance with a second change amount DFex determined to lower the temperature of the exhaust gas Means (step 850 in FIG. 8, routine in FIG. 9).

In the first device,
The air-fuel ratio is controlled at a first time point (for example, time ta, time tb or time tc in FIG. 7), and the second time point after the first time point or the first time point ( For example, the control of the air-fuel ratio and the temperature of the exhaust gas during the catalyst temperature control period, which is a period from time tc in FIG. 7 to a third time after the second time (for example, time tf in FIG. 7). When at least the temperature of the exhaust gas is controlled, the first change amount DFaf and the second change amount DFex at the fourth time point (for example, time td in FIG. 7) during the catalyst temperature control period. The first change amount DFaf and the second change amount DFex at the fourth time point are determined such that the sum of the first change amount DFaf at the first time point is equal to or greater than the first change amount DFaf at the first time point.

Furthermore, in the first device:
The catalyst temperature control period includes the current temperature Tp of the catalyst 53, which is the temperature of the catalyst 53 at the current time point, and the convergence temperature of the catalyst 53, which is the temperature estimated to reach the temperature of the catalyst 53 at a future time point. This is a period determined during the catalyst temperature control period when at least one of Tf is equal to or higher than the threshold temperature Tcatth (period determined as “Yes” in step 920 in FIG. 9).

Furthermore, in the first device:
The first change amount DFaf is a change amount based on a basic amount Fbase that is a fuel amount determined based on the target air-fuel ratio abyfr, and the second change amount DFex is a change based on the basic amount Fbase. Quantity (see step 850 of FIG. 8).

Furthermore, in the first device:
When the second change amount DFex determined at the fourth time point is smaller than the first change amount DFaf at the first time point (when determined as “Yes” in Step 1050 of FIG. 10), At the time, both the air-fuel ratio control and the exhaust gas temperature control are performed.

Furthermore, in the first device:
The target air-fuel ratio abyfr at the fourth time point is set to an air-fuel ratio smaller than the target air-fuel ratio abyfr at the first time point (see step 890 of step 8).

Then in the second device:
The target air-fuel ratio abyfr at the fourth time point is a value DFexcon obtained by dividing the sum of the second change amount DFex and the basic amount Fbase at the fourth time point by the basic amount Fbase (step 1310 in FIG. 13). The control device is an air-fuel ratio (see step 1320) obtained by dividing the target air-fuel ratio abyfr at the first time point.

Then, in the third device:
When the second change amount DFex determined at the fourth time point is smaller than the first change amount DFaf at the first time point (when it is determined “Yes” in step 1510 of FIG. 15), the second change amount DFex is determined. After the change amount DFex is corrected to an amount DFexlarge that is greater than or equal to the first change amount DFaf, only the exhaust gas temperature control of the air-fuel ratio control and the exhaust gas temperature control is performed at the fourth time point. Is called.

Then, in the fourth device:
When the second change amount DFex determined at the fourth time point is smaller than the first change amount DFaf at the first time point (when it is determined “Yes” in Step 1810 in FIG. 18), After the change amount DFex is corrected to the sum of the second change amount DFex and the first change amount DFaf (see step 1820), the control of the air-fuel ratio and the temperature of the exhaust gas at the fourth time point are performed. Of the control, only the temperature of the exhaust gas is controlled.

Next, in the fifth device:
As the second change amount DFex, the current temperature Tp of the catalyst 53 is set to a reference change amount DFexbase that is determined based on the operating state of the internal combustion engine 10 and is larger than the first change amount DFaf at the first time point. A correction change amount obtained by multiplying the correction coefficient CRex that approaches 1 as the convergence temperature Tf approaches 53 is obtained (see step 2030 in FIG. 20).

Furthermore, in the fifth device:
As the correction coefficient CRex, a value DFexcon obtained by dividing the difference between the current temperature Tp of the catalyst 53 and the threshold temperature Tcatth by the difference between the convergence temperature Tf of the catalyst 53 and the threshold temperature Tcatth is employed. (See step 2020 in FIG. 20).

By the way, in the first device to the fifth device,
As the target air-fuel ratio abyfr at the first time point, the stoichiometric air-fuel ratio stoich can be adopted (see, for example, step 810 in FIG. 8).

Furthermore, in the first device to the fifth device,
The catalyst 53 when the oxygen concentration of the exhaust gas deviates from the reference oxygen concentration, which is the oxygen concentration of the exhaust gas generated when the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio stoich, in the direction in which the oxygen concentration increases. When the purification rate of nitrogen oxides NOx contained in the exhaust gas by 53 decreases at the first reduction rate, and the oxygen concentration of the exhaust gas moves away from the reference oxygen concentration in a direction in which the oxygen concentration decreases. A catalyst having a characteristic that the purification rate of nitrogen oxides NOx decreases at a second reduction rate smaller than the first reduction rate may be employed.

<Other aspects>
The present invention is not limited to the above embodiments, and various modifications can be adopted within the scope of the present invention.

  For example, the control devices according to the above embodiments employ the stoichiometric air-fuel ratio stoich as the upstream target air-fuel ratio abyfr. However, the control device of the present invention can be configured to employ an air-fuel ratio other than the stoichiometric air-fuel ratio stoich as the upstream target air-fuel ratio abyfr. That is, the control device of the present invention may be set to an appropriate value considering the exhaust gas purification performance of the catalyst.

  Furthermore, the control device according to each of the above embodiments estimates the current temperature Tp of the catalyst 53 based on the convergence temperature Tf (see, for example, step 920 in FIG. 9). However, the control device of the present invention may be configured to acquire the current temperature of the catalyst by a sensor capable of measuring the temperature of the catalyst.

  Furthermore, the control device according to each of the above embodiments includes only one injector. However, the control device of the present invention can include a plurality of injectors. For example, the engine 10 may include an air-fuel ratio control injector and an exhaust gas temperature control injector. That is, the internal combustion engine to which the control device of the present invention is applied only needs to have a configuration capable of changing the final amount of fuel supplied to the internal combustion engine (that is, introduced into the combustion chamber).

  Furthermore, the control device according to each of the above embodiments is applied to an engine (spark ignition type engine) provided with a three-way catalyst. However, the control device of the present invention can also be applied to an engine (for example, a diesel engine) provided with a NOx storage reduction catalyst.

  Furthermore, the control device according to each of the above embodiments includes only one catalyst. However, the control device of the present invention can be applied to an engine including a plurality of catalysts.

  By the way, in the control devices according to the above embodiments, the air-fuel ratio of the catalyst introduction gas is always equal to or lower than the stoichiometric air-fuel ratio stoich when the exhaust gas temperature control is performed in consideration of the fuel cooling effect and the NOx emission amount (rich side). The air-fuel ratio related variation amount DFaf and the exhaust gas temperature related variation amount DFex are determined. However, as far as the NOx emission amount is concerned, there are cases where the air-fuel ratio of the catalyst introduction gas is allowed to be larger than the stoichiometric air-fuel ratio stoich (the lean air-fuel ratio).

  More specifically, the catalyst 53 has an oxygen storage capability (when the air-fuel ratio of the catalyst introduction gas is the lean air-fuel ratio, the catalyst 53 stores oxygen in the gas, and the air-fuel ratio of the catalyst introduction gas is rich). If the catalyst 53 has sufficient capacity to store oxygen, the air-fuel ratio of the catalyst introduction gas is equal to the lean-side air-fuel ratio. Even if it exists, it is thought that NOx discharge | emission amount does not increase in the period when the catalyst 53 can occlude oxygen.

  Accordingly, examples of the control device applied to the internal combustion engine including the catalyst having such characteristics include the following control devices.

A catalyst for purifying exhaust gas from an internal combustion engine, wherein the oxygen concentration of the catalyst introduction gas, which is exhaust gas introduced into the catalyst, is the oxygen concentration of the gas generated when air and fuel burn at the stoichiometric air-fuel ratio When the oxygen concentration is higher than the oxygen concentration, the oxygen in the catalyst introduction gas is occluded in the catalyst, and when the oxygen concentration of the catalyst introduction gas is lower than the reference oxygen concentration, the oxygen occluded in the catalyst is A catalyst having a characteristic that the oxygen concentration of the exhaust gas in the catalyst approaches the reference oxygen concentration by being released into the catalyst introduction gas;
Applied to an internal combustion engine with
Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, which is supplied to the internal combustion engine according to a first change amount determined so as to match the air-fuel ratio with a target air-fuel ratio. An air-fuel ratio control means for changing the amount of fuel;
Exhaust gas temperature control means for controlling the temperature of the exhaust gas, the exhaust gas temperature control means for changing the amount of fuel supplied to the internal combustion engine in accordance with a second change amount determined to lower the temperature of the exhaust gas; ,
An internal combustion engine control device comprising:
The air-fuel ratio is controlled at the first time point, and in the period from the first time point or the second time point after the first time point to the third time point after the second time point. When at least the exhaust gas temperature control among the air-fuel ratio control and the exhaust gas temperature control is performed during a certain catalyst temperature control period, the second time determined at the fourth time point during the catalyst temperature control period. When the change amount is smaller than the first change amount at the first time point, and the oxygen concentration of the catalyst exhaust gas that is the exhaust gas discharged from the catalyst at the fourth time point is greater than the reference oxygen concentration, the internal combustion engine A reference change amount that is determined based on the operating state of the engine and is larger than the first change amount at the first time point is adopted as the second change amount, and oxygen of the catalyst exhaust gas at the fourth time point is used. If the degree is equal to or less than the reference oxygen concentration, a correction change amount obtained by multiplying a reference change amount by a correction coefficient that approaches 1 as the temperature of the catalyst approaches the convergence temperature of the catalyst is adopted as the second change amount. To be
Control device for internal combustion engine.

  According to the above control device, when the oxygen concentration of the catalyst exhaust gas is equal to or lower than the reference oxygen concentration (when the air-fuel ratio of the catalyst exhaust gas is the stoichiometric air-fuel ratio or the air-fuel ratio on the rich side), "Change amount" is adopted. When this correction change amount is employed, the sum of the first change amount and the second change amount during the catalyst temperature control period (fourth time point) is the first change amount before the catalyst temperature control period (first time point). It may not be more. That is, the air-fuel ratio of the catalyst introduction gas may become the lean air-fuel ratio. However, if the air-fuel ratio of the catalyst exhaust gas is “the stoichiometric air-fuel ratio or rich air-fuel ratio”, it is considered that the catalyst has sufficient remaining capacity to store oxygen. Even if the air-fuel ratio is on the lean side, the NOx emission amount is considered not to increase during the period in which the catalyst can store oxygen.

  As a result, the control device can appropriately perform both the control of the exhaust gas temperature and the control of the air-fuel ratio (in particular, the control of the air-fuel ratio) in the catalyst temperature control period.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 25 ... Combustion chamber, 34 ... Injector, 53 ... Catalyst, 76 ... Upstream air-fuel ratio sensor, 77 ... Downstream air-fuel ratio sensor, 80 ... Electronic control unit

Claims (12)

Applied to an internal combustion engine equipped with a catalyst for purifying exhaust gas of the internal combustion engine,
Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, which is supplied to the internal combustion engine according to a first change amount determined so as to match the air-fuel ratio with a target air-fuel ratio. An air-fuel ratio control means for changing the amount of fuel;
Exhaust gas temperature control means for controlling the temperature of the exhaust gas, the exhaust gas temperature control means for changing the amount of fuel supplied to the internal combustion engine in accordance with a second change amount determined to lower the temperature of the exhaust gas; ,
An internal combustion engine control device comprising:
The air-fuel ratio is controlled at the first time point, and in the period from the first time point or the second time point after the first time point to the third time point after the second time point. When at least the exhaust gas temperature control among the air-fuel ratio control and the exhaust gas temperature control is performed during a catalyst temperature control period, the first change amount at the fourth time point in the catalyst temperature control period And the second change amount are determined such that the first change amount and the second change amount at the fourth time point are equal to or greater than the first change amount at the first time point.
Control device for internal combustion engine. The control device according to claim 1,
The catalyst temperature control period is at least a current temperature of the catalyst that is the temperature of the catalyst at a current time point, and a convergence temperature of the catalyst that is a temperature that is estimated to reach the temperature of the catalyst at a future time point A control device that is a period in which one is determined to be equal to or higher than a threshold temperature during the catalyst temperature control period. In the control device according to claim 1 or 2,
The control device wherein the first change amount is a change amount based on a basic amount which is a fuel amount determined based on the target air-fuel ratio, and the second change amount is a change amount based on the basic amount. . In the control device according to any one of claims 1 to 3,
When the second change amount determined at the fourth time point is smaller than the first change amount at the first time point, both the air-fuel ratio control and the exhaust gas temperature control are performed at the fourth time point. Control device. The control device according to claim 4,
The control device, wherein the target air-fuel ratio at the fourth time point is smaller than the target air-fuel ratio at the first time point. The control device according to claim 5,
The target air-fuel ratio at the first time point is determined by the value obtained by dividing the sum of the second change amount and the basic amount at the fourth time point by the basic amount. A control device that is an air-fuel ratio obtained by division. In the control device according to any one of claims 1 to 3,
When the second change amount determined at the fourth time point is smaller than the first change amount at the first time point, the second change amount is corrected to an amount equal to or greater than the first change amount, and The control device in which only the control of the temperature of the exhaust gas among the control of the air-fuel ratio and the control of the temperature of the exhaust gas is performed at a fourth time point. In the control device according to any one of claims 1 to 3,
When the second change amount determined at the fourth time point is smaller than the first change amount at the first time point, the second change amount is corrected to the sum of the second change amount and the first change amount. Then, at the fourth time point, only the temperature control of the exhaust gas among the control of the air-fuel ratio and the control of the temperature of the exhaust gas is performed. In the control device according to any one of claims 1 to 8,
The second change amount is determined based on the operating state of the internal combustion engine, and the reference change amount that is larger than the first change amount at the first time point is such that the current temperature of the catalyst approaches the convergence temperature of the catalyst. A control device, which is a correction change amount obtained by multiplying a correction coefficient approaching 1. The control device according to claim 9,
The control device, wherein the correction coefficient is a value obtained by dividing the difference between the current temperature of the catalyst and the threshold temperature by the difference between the convergence temperature of the catalyst and the threshold temperature. In the control device according to any one of claims 1 to 10,
A control device in which the target air-fuel ratio at the first time point is a stoichiometric air-fuel ratio. In the control device according to any one of claims 1 to 11,
When the oxygen concentration of the exhaust gas deviates in a direction in which the oxygen concentration increases from the reference oxygen concentration that is the oxygen concentration of the exhaust gas generated when the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio, the catalyst causes the catalyst When the purification rate of nitrogen oxides contained in the exhaust gas decreases at the first reduction rate, and the oxygen concentration of the exhaust gas moves away from the reference oxygen concentration in a direction in which the oxygen concentration decreases, the nitrogen oxides A control device that is a catalyst having a characteristic that a purification rate decreases at a second reduction rate that is smaller than the first reduction rate.

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